Set minimum Ruby version, update README, add "-alpha" version designation

.travis.yml

@@ -2,11 +2,12 @@
 language: ruby
 
 rvm:
-  - 2.2
-  - jruby-9.0.0.0
+  - 2.2.2
+  - 2.2.3
   - ruby-head
-  - jruby-head
   - rbx-2
+  - jruby-9.0.0.0
+  - jruby-head
 
 sudo: false
 

README.md

@@ -2871,31 +2871,10 @@ thin --threaded start
 
 The following Ruby versions are officially supported:
 <dl>
-  <dt>Ruby 1.8.7</dt>
+  <dt>Ruby 2.2.2+</dt>
   <dd>
-    1.8.7 is fully supported, however, if nothing is keeping you from it, we
-    recommend upgrading or switching to JRuby or Rubinius. Support for 1.8.7
-    will not be dropped before Sinatra 2.0. Ruby 1.8.6 is no longer supported.
-  </dd>
-
-  <dt>Ruby 1.9.2</dt>
-  <dd>
-    1.9.2 is fully supported. Do not use 1.9.2p0, as it is known to cause
-    segmentation faults when running Sinatra. Official support will continue
-    at least until the release of Sinatra 1.5.
-  </dd>
-
-  <dt>Ruby 1.9.3</dt>
-  <dd>
-    1.9.3 is fully supported and recommended. Please note that switching to 1.9.3
-    from an earlier version will invalidate all sessions. 1.9.3 will be supported
-    until the release of Sinatra 2.0.
-  </dd>
-
-  <dt>Ruby 2.x</dt>
-  <dd>
-    2.x is fully supported and recommended. There are currently no plans to drop
-    official support for it.
+    2.2.2 is fully supported and recommended. There are currently no plans to
+    drop official support for it.
   </dd>
 
   <dt>Rubinius</dt>
@@ -2912,6 +2891,8 @@ The following Ruby versions are officially supported:
   </dd>
 </dl>
 
+Versions of Ruby prior to 2.2.2 are no longer supported as of Sinatra 2.0.
+
 We also keep an eye on upcoming Ruby versions.
 
 The following Ruby implementations are not officially supported but still are

lib/sinatra/version.rb

@@ -1,3 +1,3 @@
 module Sinatra
-  VERSION = '2.0.0'
+  VERSION = '2.0.0-alpha'
 end

sinatra.gemspec

@@ -13,6 +13,8 @@ Gem::Specification.new 'sinatra', Sinatra::VERSION do |s|
   s.extra_rdoc_files  = s.files.select { |p| p =~ /^README/ } << 'LICENSE'
   s.rdoc_options      = %w[--line-numbers --inline-source --title Sinatra --main README.rdoc --encoding=UTF-8]
 
+  s.required_ruby_version = '>= 2.2.2'
+
   s.add_dependency 'rack', '>= 1.6'
   s.add_dependency 'tilt', '~> 2.0'
   s.add_dependency 'rack-protection', '~> 1.5'