Specify simple JSON request body even if empty.

Otherwise response from Github is 400 -- "Cannot parse JSON"

Author: noahd1

lib/cc/services/github_pull_requests.rb

@@ -26,7 +26,7 @@ class Config < CC::Service::Config
   def receive_test
     setup_http
 
-    http_post(base_status_url("0" * 40))
+    http_post(base_status_url("0" * 40), "{}")
 
   rescue HTTPError => ex
     if ex.status == 422 # response message: "No commit found for SHA"