Load 'json' gem even on 1.9.3

I've found problems running JSON on Ubuntu 14.04 even it seems like for
ruby 1.9.3 JSON class should be loaded by default. Better meake sure it
is loaded by forcing `require 'json'` in the begging of the providers.

Change-Id: Ia01822b30d0a8a9f391fcd4f56b76bb7ce039258

lib/puppet/provider/midonet_gateway/midonet_api_caller.rb

@@ -1,11 +1,11 @@
-require 'uri'
-require 'faraday'
-
 if RUBY_VERSION == '1.8.7'
     require 'rubygems'
-    require 'json'
 end
 
+require 'uri'
+require 'faraday'
+require 'json'
+
 Puppet::Type.type(:midonet_gateway).provide(:midonet_api_caller) do
 
   def create

lib/puppet/provider/midonet_host_registry/midonet_api_caller.rb

@@ -1,12 +1,11 @@
-require 'uri'
-require 'faraday'
-# Host registry type
-
 if RUBY_VERSION == '1.8.7'
   require 'rubygems'
-  require 'json'
 end
 
+require 'uri'
+require 'faraday'
+require 'json'
+
 Puppet::Type.type(:midonet_host_registry).provide(:midonet_api_caller) do
 
   def create