Gradle update and small fixes

* Really old version of Gradle was used in this project. I updated it to latest stable, since `build.gradle` is preatty simple everything works as usual. Also removed `.gradle` directory
* Fixed mileading exception meassage in `org.encog.neural.flat.FlatNetwork.decodeNetwork()` and added test for it
* Added `.travis.yml` to integrate with [travis-ci](https://travis-ci.org/janisz/encog-java-core/builds)