Bump json-schema version to 2.2.3

This is to pick up our fix to the gem for symbol keys in hashes in
arrays:

    voxpupuli/json-schema#105

This means that we can write our test data more idiomatically as ruby
hashes with symbol keys. While working on the schema we had found a
workaround to this which involved calling .to_json on the data before
validating it, but the fix makes this unnecessary.

Gemfile

@@ -5,7 +5,7 @@ gem 'rails-api', '0.2.1'
 gem 'logstasher', '0.5.3'
 gem 'unicorn', '4.8.3'
 gem 'airbrake', '3.1.15'
-gem 'json-schema', '2.2.2'
+gem 'json-schema', '2.2.3'
 
 group :development, :test do
   gem 'rspec-rails', '3.0.1'

Gemfile.lock

@@ -43,7 +43,7 @@ GEM
     hike (1.2.3)
     i18n (0.6.9)
     json (1.8.1)
-    json-schema (2.2.2)
+    json-schema (2.2.3)
     kgio (2.9.2)
     logstash-event (1.1.5)
     logstasher (0.5.3)
@@ -136,7 +136,7 @@ DEPENDENCIES
   airbrake (= 3.1.15)
   ci_reporter (= 2.0.0.alpha2)
   ci_reporter_rspec (= 0.0.2)
-  json-schema (= 2.2.2)
+  json-schema (= 2.2.3)
   logstasher (= 0.5.3)
   rails (= 4.1.2)
   rails-api (= 0.2.1)