Add test for colon in final path segment not meant as verb

See grpc-ecosystem#224

Signed-off-by: James Hamlin <james@goforward.com>

runtime/mux_test.go

@@ -176,6 +176,22 @@ func TestMuxServeHTTP(t *testing.T) {
 			respStatus:  http.StatusOK,
 			respContent: "POST /foo:bar",
 		},
+		{
+			patterns: []stubPattern{
+				{
+					method: "POST",
+					ops:    []int{int(utilities.OpLitPush), 0},
+					pool:   []string{"foo"},
+				},
+			},
+			reqMethod: "POST",
+			reqPath:   "/foo:bar",
+			headers: map[string]string{
+				"Content-Type": "application/json",
+			},
+			respStatus:  http.StatusOK,
+			respContent: "POST /foo:bar",
+		},
 	} {
 		mux := runtime.NewServeMux()
 		for _, p := range spec.patterns {