Use same version constraint in mysql adapter and generated application

Follow up of 924a368f

railties/lib/rails/generators/app_base.rb

@@ -297,7 +297,7 @@ def rails_version_specifier(gem_version = Rails.gem_version)
       def gem_for_database
         # %w( mysql postgresql sqlite3 oracle frontbase ibm_db sqlserver jdbcmysql jdbcsqlite3 jdbcpostgresql )
         case options[:database]
-        when "mysql"          then ["mysql2", [">= 0.3.18", "< 0.5"]]
+        when "mysql"          then ["mysql2", ["~> 0.4.4"]]
         when "postgresql"     then ["pg", ["~> 0.18"]]
         when "oracle"         then ["activerecord-oracle_enhanced-adapter", nil]
         when "frontbase"      then ["ruby-frontbase", nil]

railties/test/generators/app_generator_test.rb

@@ -404,7 +404,7 @@ def test_config_another_database
     if defined?(JRUBY_VERSION)
       assert_gem "activerecord-jdbcmysql-adapter"
     else
-      assert_gem "mysql2", "'>= 0.3.18', '< 0.5'"
+      assert_gem "mysql2", "'~> 0.4.4'"
     end
   end