tool/merger.rb: Avoid making too-deep indentation

because it's hard to understand what's going on when indentation depth
is too deep.

Sorry for polluting git blame, but most of the Merger's lines are
updated recently anyway.

tool/merger.rb

@@ -16,10 +16,11 @@ ENV['LC_ALL'] = 'C'
 
 module Merger
   REPOS = 'svn+ssh://svn@ci.ruby-lang.org/ruby/'
+end
 
-  class << self
+class << Merger
   def help
-      puts <<-end
+    puts <<-HELP
 \e[1msimple backport\e[0m
   ruby #$0 1234
 
@@ -45,7 +46,7 @@ module Merger
   ruby #$0 removetag 2.2.9
 
 \e[33;1m* all operations shall be applied to the working directory.\e[0m
-      end
+    HELP
   end
 
   def interactive(str, editfile = nil)
@@ -229,8 +230,7 @@ module Merger
     puts "+ #{cmd.shelljoin}"
     system(*cmd)
   end
-  end # class << self
-end # module Merger
+end
 
 case ARGV[0]
 when "teenyup"