like this?

Author: korny

Gemfile

@@ -7,7 +7,7 @@ gemspec
 # Include everything needed to run rake, tests, features, etc.
 group :development do
   gem 'bundler'
-  gem 'json', '>= 1.8' if RUBY_VERSION < '2.0'
+  gem 'json', '~> 1.8' if RUBY_VERSION < '2.0'
   gem 'rake',             RUBY_VERSION < '1.9' ? '~> 10.5'    : '>= 10.5'
   gem 'rdoc',             Gem::Version.new(RUBY_VERSION) < Gem::Version.new('1.9.3') ? '~> 4.2.2' : Gem::Version.new(RUBY_VERSION) < Gem::Version.new('2.2.2') ? '< 6' : '>= 6'
   gem 'RedCloth',         RUBY_PLATFORM == 'java' ? '= 4.2.9' : '>= 4.0.3'