Use maven wrapper to lock mvn version (#172)

* enable mvnw

Signed-off-by: Yan Zhang <[email protected]>

* use trusty

Signed-off-by: Yan Zhang <[email protected]>

Author: Eskibear

.travis.yml

@@ -7,6 +7,7 @@ os:
 - linux
 - osx
 
+dist: trusty
 osx_image: xcode9.3
 
 before_install:

gulpfile.js

@@ -33,6 +33,5 @@ function isLinux() {
 }
 
 function mvnw() {
-  return "mvn";
-    // return isWin()?"mvnw.cmd":"./mvnw";
+    return isWin()?"mvnw.cmd":"./mvnw";
 }