update go-marathon to 441a03a

in order to get the latest fixes regarding SSE subscription failover.

vendor/github.com/gambol99/go-marathon/client.go

@@ -190,6 +190,11 @@ type httpClient struct {
 	config Config
 }
 
+// newRequestError signals that creating a new http.Request failed
+type newRequestError struct {
+	error
+}
+
 // NewClient creates a new marathon client
 //		config:			the configuration to use
 func NewClient(config Config) (Marathon, error) {
@@ -317,7 +322,8 @@ func (r *marathonClient) apiCall(method, path string, body, result interface{})
 	}
 }
 
-// buildAPIRequest creates a default API request
+// buildAPIRequest creates a default API request.
+// It fails when there is no available member in the cluster anymore or when the request can not be built.
 func (r *marathonClient) buildAPIRequest(method, path string, reader io.Reader) (request *http.Request, member string, err error) {
 	// Grab a member from the cluster
 	member, err = r.hosts.getMember()
@@ -328,7 +334,7 @@ func (r *marathonClient) buildAPIRequest(method, path string, reader io.Reader)
 	// Build the HTTP request to Marathon
 	request, err = r.client.buildMarathonRequest(method, member, path, reader)
 	if err != nil {
-		return nil, member, err
+		return nil, member, newRequestError{err}
 	}
 	return request, member, nil
 }