Switch to maven wrapper 
Switch to maven wrapper 

Trying to fix:
```
[ERROR] Failed to execute goal org.codehaus.mojo:license-maven-plugin:2.0.0:check-file-header (check-license) on project graphwalker-project: The plugin org.codehaus.mojo:license-maven-plugin:2.0.0 requires Maven version 3.5.4 -> [Help 1]
```
when building on travis-ci
KristianKarl/graphwalker-project,GraphWalker/graphwalker-project,GraphWalker/graphwalker-project,GraphWalker/graphwalker-project,KristianKarl/graphwalker-project,KristianKarl/graphwalker-project