Remove trailing slashes from appservice url (#546)

* Remove trailing slashes from appservice url

* Use TrimRight instead

src/github.com/matrix-org/dendrite/common/config/appservice.go

@@ -236,6 +236,9 @@ func checkErrors(config *Dendrite) (err error) {
 			}
 		}
 
+		// Check if the url has trailing /'s. If so, remove them
+		appservice.URL = strings.TrimRight(appservice.URL, "/")
+
 		// Check if we've already seen this ID. No two application services
 		// can have the same ID or token.
 		if idMap[appservice.ID] {