Updated CHANGELOG.md for version 1.3.1 release
Release v1.4.0 (Master)
* Implemented x-arango-version. Closes #160.
There is a minor backward incompatibility. We are now following ArangoDB's integer version numbering style.
Instead of 1.4.0 we return 10400 when calling the Connection::getVersion() / getClientVersion() method.
This has hopefully not any enormous impact. If it has please inform me so we can find a better solution...