Trim tailing slash from service name before proxy

**What**
- When determining the service name of the function, remove any trailing
slashes, the slashes are not allowed in service names for either Swarm
or K8S, so this can only be a left over from the url path

**Why**
- This was preventing service resolution, and hence failed functions,
    when the function was called with a trailing slash

Fixes #714

Signed-off-by: Lucas Roesler <roesler.lucas@gmail.com>

gateway/handlers/forwarding_proxy.go

@@ -133,7 +133,7 @@ func getServiceName(urlValue string) string {
 	if strings.HasPrefix(urlValue, forward) {
 		serviceName = urlValue[len(forward):]
 	}
-	return serviceName
+	return strings.Trim(serviceName, "/")
 }
 
 // LoggingNotifier notifies a log about a request
@@ -168,7 +168,6 @@ type FunctionAsHostBaseURLResolver struct {
 
 // Resolve the base URL for a request
 func (f FunctionAsHostBaseURLResolver) Resolve(r *http.Request) string {
-
 	svcName := getServiceName(r.URL.Path)
 
 	const watchdogPort = 8080