diff --git a/.travis.yml b/.travis.yml
index 5d9a377..d7eaa59 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -5,7 +5,7 @@ rvm:
   - 2.3
   - 2.4
   - 2.5
-  - ruby-head
+  - 2.6
 
 before_install:
   - gem install bundler
@@ -22,10 +22,9 @@ gemfile:
 
 matrix:
   include:
-    - rvm: ruby-head
+    - rvm: 2.6
       env: RUBYOPT="--enable-frozen-string-literal"
-  # allow_failures:
-  #   - rvm: ruby-head
+      gemfile: gemfiles/rails_5.2.gemfile
 
 addons:
   code_climate:
diff --git a/Appraisals b/Appraisals
index 82d15ad..a98e42a 100644
--- a/Appraisals
+++ b/Appraisals
@@ -8,6 +8,7 @@
 
 appraise 'rails-5.0' do
   gem 'rails', '>= 5.0.0', '< 5.1'
+  gem 'sqlite3', '~> 1.3.6'
 end
 
 appraise 'rails-5.1' do
diff --git a/gemfiles/rails_5.0.gemfile b/gemfiles/rails_5.0.gemfile
index 4c5cb4b..4f212f0 100644
--- a/gemfiles/rails_5.0.gemfile
+++ b/gemfiles/rails_5.0.gemfile
@@ -3,5 +3,6 @@
 source "https://rubygems.org"
 
 gem "rails", ">= 5.0.0", "< 5.1"
+gem "sqlite3", "~> 1.3.6"
 
 gemspec path: "../"
diff --git a/lib/awesome_print/ext/active_record.rb b/lib/awesome_print/ext/active_record.rb
index 2a4a362..0b7d9d6 100644
--- a/lib/awesome_print/ext/active_record.rb
+++ b/lib/awesome_print/ext/active_record.rb
@@ -55,7 +55,7 @@ module AwesomePrint
                  hash
                end
              end
-      "#{object} " << awesome_hash(data)
+      "#{object} #{awesome_hash(data)}"
     end
 
     # Format ActiveRecord class object.
@@ -95,7 +95,7 @@ module AwesomePrint
              end
 
       data.merge!({details: object.details, messages: object.messages})
-      "#{object} " << awesome_hash(data)
+      "#{object} #{awesome_hash(data)}"
     end
   end
 end
diff --git a/lib/awesome_print/formatters/array_formatter.rb b/lib/awesome_print/formatters/array_formatter.rb
index 3340a77..4c96284 100644
--- a/lib/awesome_print/formatters/array_formatter.rb
+++ b/lib/awesome_print/formatters/array_formatter.rb
@@ -31,7 +31,7 @@ module AwesomePrint
         if options[:multiline]
           multiline_array
         else
-          '[ ' << array.map { |item| inspector.awesome(item) }.join(', ') << ' ]'
+          "[ #{array.map { |item| inspector.awesome(item) }.join(', ')} ]"
         end
       end
 
diff --git a/lib/awesome_print/formatters/hash_formatter.rb b/lib/awesome_print/formatters/hash_formatter.rb
index c29bb63..30bbcd4 100644
--- a/lib/awesome_print/formatters/hash_formatter.rb
+++ b/lib/awesome_print/formatters/hash_formatter.rb
@@ -73,7 +73,7 @@ module AwesomePrint
 
         keys.map! do |key|
           plain_single_line do
-            [inspector.awesome(key), hash[key]]
+            [String.new(inspector.awesome(key)), hash[key]]
           end
         end
       end
diff --git a/lib/awesome_print/formatters/object_formatter.rb b/lib/awesome_print/formatters/object_formatter.rb
index 49334f7..eca30d6 100644
--- a/lib/awesome_print/formatters/object_formatter.rb
+++ b/lib/awesome_print/formatters/object_formatter.rb
@@ -22,7 +22,7 @@ module AwesomePrint
             object.respond_to?(property) ? :reader : nil
           end
           if accessor
-            ["attr_#{accessor} :#{property}", var]
+            [String.new("attr_#{accessor} :#{property}"), var]
           else
             [var.to_s, var]
           end
@@ -60,7 +60,8 @@ module AwesomePrint
       end
 
       def awesome_instance
-        str = object.send(options[:class_name]).to_s
+        str = String.new
+        str << object.send(options[:class_name]).to_s
         str << ":0x%08x" % (object.__id__ * 2) if options[:object_id]
         str
       end
diff --git a/spec/formats_spec.rb b/spec/formats_spec.rb
index 9427b44..ac83732 100644
--- a/spec/formats_spec.rb
+++ b/spec/formats_spec.rb
@@ -492,7 +492,7 @@ EOS
   describe 'File' do
     it 'should display a file (plain)' do
       File.open(__FILE__, 'r') do |f|
-        expect(f.ai(plain: true)).to eq("#{f.inspect}\n" << `ls -alF #{f.path}`.chop)
+        expect(f.ai(plain: true)).to eq("#{f.inspect}\n#{`ls -alF #{f.path}`.chop}")
       end
     end
   end
@@ -501,7 +501,7 @@ EOS
   describe 'Dir' do
     it 'should display a direcory (plain)' do
       Dir.open(File.dirname(__FILE__)) do |d|
-        expect(d.ai(plain: true)).to eq("#{d.inspect}\n" << `ls -alF #{d.path}`.chop)
+        expect(d.ai(plain: true)).to eq("#{d.inspect}\n#{`ls -alF #{d.path}`.chop}")
       end
     end
   end
@@ -694,7 +694,7 @@ EOS
       class My < File; end
 
       my = File.new('/dev/null') rescue File.new('nul')
-      expect(my.ai(plain: true)).to eq("#{my.inspect}\n" << `ls -alF #{my.path}`.chop)
+      expect(my.ai(plain: true)).to eq("#{my.inspect}\n#{`ls -alF #{my.path}`.chop}")
     end
 
     it 'inherited from Dir should be displayed as Dir' do
@@ -702,7 +702,7 @@ EOS
 
       require 'tmpdir'
       my = My.new(Dir.tmpdir)
-      expect(my.ai(plain: true)).to eq("#{my.inspect}\n" << `ls -alF #{my.path}`.chop)
+      expect(my.ai(plain: true)).to eq("#{my.inspect}\n#{`ls -alF #{my.path}`.chop}")
     end
 
     it 'should handle a class that defines its own #send method' do