update grape to 0.3.1 for ruby 2.0 support.

add grape-entity, that is split from grape 0.3.0.
remove usage of deprecated error_format, that is removed in grape 0.2.3.

Gemfile

@@ -39,7 +39,8 @@ gem "pygments.rb",  git: "https://github.com/gitlabhq/pygments.rb.git", branch:
 gem "github-linguist", "~> 2.3.4" , require: "linguist"
 # API
-gem "grape", "~> 0.2.1"
+gem "grape", "~> 0.3.1"
+gem "grape-entity", "~> 0.2.0"
 # Format dates and times
 # based on human-friendly examples

Gemfile.lock

@@ -182,8 +182,9 @@ GEM
       pyu-ruby-sasl (~> 0.0.3.1)
       rubyntlm (~> 0.1.1)
     gitlab_yaml_db (1.0.0)
-    grape (0.2.2)
+    grape (0.3.1)
       activesupport
+      grape-entity (~> 0.2.0)
       hashie (~> 1.2)
       multi_json (>= 1.3.2)
       multi_xml
@@ -191,6 +192,7 @@ GEM
       rack-accept
       rack-mount
       virtus
+    grape-entity (0.2.0)
     growl (1.0.3)
     guard (1.5.4)
       listen (>= 0.4.2)
@@ -481,7 +483,8 @@ DEPENDENCIES
   gitlab_omniauth-ldap (= 1.0.2)
   gitlab_yaml_db (= 1.0.0)
   grack!
-  grape (~> 0.2.1)
+  grape (~> 0.3.1)
+  grape-entity (~> 0.2.0)
   grit!
   grit_ext!
   growl

lib/api.rb

@@ -9,7 +9,6 @@ class API < Grape::API
     end
     format :json
-    error_format :json
     helpers APIHelpers
     
     mount Groups