Use `methods: :any` in our rack-cors configuration

This was added in rack-cors 0.4.0 and allows all types of CORS requests
to the API.

config/application.rb

@@ -74,7 +74,7 @@ module Gitlab
         origins '*'
         resource '/api/*',
           headers: :any,
-          methods: [:get, :post, :options, :put, :delete],
+          methods: :any,
           expose: ['Link']
       end
     end