updates rollbar

Gemfile.lock

@@ -239,7 +239,6 @@ GEM
       multi_json (~> 1.3)
       multi_xml (~> 0.5)
       rack (~> 1.2)
-    oj (2.12.14)
     omniauth (1.2.2)
       hashie (>= 1.2, < 4)
       rack (~> 1.0)
@@ -309,8 +308,8 @@ GEM
       mime-types (>= 1.16, < 3.0)
       netrc (~> 0.7)
     rinku (1.7.3)
-    rollbar (2.3.0)
-      oj (~> 2.12.14)
+    rollbar (2.4.0)
+      multi_json
     rspec (3.3.0)
       rspec-core (~> 3.3.0)
       rspec-expectations (~> 3.3.0)
@@ -461,7 +460,7 @@ DEPENDENCIES
   rails (= 4.2.4)
   responders
   rinku
-  rollbar (~> 2.3.0)
+  rollbar (~> 2.4.0)
   rspec-rails (~> 3.0)
   sass-rails (~> 5.0)
   savon