Fix build URL in Discord reporter (#503)

Author: zware

master/custom/discord_reporter.py

@@ -141,7 +141,7 @@ def sendMessage(self, reports):
 
     def _getURLForBuild(self, builderid, build_number):
         prefix = self.master.config.buildbotURL
-        return prefix + "#builders/%d/builds/%d" % (builderid, build_number)
+        return prefix + "#/builders/%d/builds/%d" % (builderid, build_number)
 
     def createReport(
         self,