updates gem dependencies

fixes "pessimistic dependency on ... may be overly strict" and
"open-ended dependency on ... is not recommended" warnings

Author: sfroehler

shipcloud.gemspec

@@ -18,10 +18,10 @@ Gem::Specification.new do |spec|
   spec.test_files    = spec.files.grep(%r{^(test|spec|features)/})
   spec.require_paths = ["lib"]
 
-  spec.add_dependency "json"
+  spec.add_runtime_dependency 'json', '~> 1.8', '>= 1.8.0'
   spec.add_development_dependency 'bundler', '>= 1.3.0', '< 2.0'
-  spec.add_development_dependency 'rake', '~> 10.3.0'
-  spec.add_development_dependency 'rspec', '~> 2.99.0'
-  spec.add_development_dependency 'webmock', '~> 1.18.0'
-  spec.add_development_dependency 'pry', '~> 0.10.0'
+  spec.add_development_dependency 'rake', '~> 10.3'
+  spec.add_development_dependency 'rspec', '~> 2.99'
+  spec.add_development_dependency 'webmock', '~> 1.18'
+  spec.add_development_dependency 'pry', '~> 0.10'
 end