Fix rest-api vulnerability

Author: tmilewski

Gemfile

@@ -7,7 +7,7 @@ group :test do
   gem "json", :platforms => [:jruby, :ruby_18, :ruby_19]
   gem "mime-types", "~> 1.25", :platforms => [:jruby, :ruby_18]
   gem "rack-test"
-  gem "rest-client", "~> 1.6.0", :platforms => [:jruby, :ruby_18]
+  gem "rest-client", "~> 1.7.3", :platforms => [:jruby, :ruby_18]
   gem "rspec", "~> 3.2"
   gem "rubocop", ">= 0.30", :platforms => [:ruby_19, :ruby_20, :ruby_21, :ruby_22]
   gem "simplecov", ">= 0.9"