DMAP-45 - Prepare BrowserMap module for ASF releases

* added DISCLAIMER file
* updated package.json with correct information regarding the module's GitHub repository
* prepared the Gruntfile.js for easily creating release artifacts
* updated the travis.yml file for specifying a more up-to-date node.js version used for the build process

git-svn-id: https://svn.apache.org/repos/asf/incubator/devicemap/trunk/browsermap/trunk@1610823 13f79535-47bb-0310-9956-ffa450edef68