Fix test description

Author: Josh Murphy

spec/grape/endpoint_spec.rb

@@ -941,7 +941,7 @@ def app
       end
     end
 
-    it 'responds with a 406 for an unsupported content-type' do
+    it 'responds with a 415 for an unsupported content-type' do
       subject.format :json
       # subject.content_type :json, "application/json"
       subject.put '/request_body' do