Actually camelize the error keys

Error keys were arriving on models with underscores e.g.

    human.errors.first_name

Addresses the test which was incorrectly passing

packages/activemodel-adapter/lib/system/active-model-adapter.js

@@ -6,6 +6,7 @@ import {pluralize} from "ember-inflector";
   @module ember-data
 */
 
+var camelize = Ember.String.camelize;
 var decamelize = Ember.String.decamelize;
 var underscore = Ember.String.underscore;
 
@@ -143,6 +144,16 @@ var ActiveModelAdapter = RESTAdapter.extend({
     if (jqXHR && jqXHR.status === 422) {
       var response = Ember.$.parseJSON(jqXHR.responseText);
       var errors = response.errors ? response.errors : response;
+
+      for (var underscoredError in errors) {
+        var camelizedError = camelize(underscoredError);
+
+        if (camelizedError !== underscoredError) {
+          errors[camelizedError] = errors[underscoredError];
+          delete errors[underscoredError];
+        }
+      }
+
       return new InvalidError(errors);
     } else {
       return error;