Updated thrift version.

[gareth-robinson]

The older verson of thrift used by this library was using a version of thrift that had 'nodeunit' as a dependency, when it should have been a devDependency. This meant that a lot of test libraries ended up bloating production builds using this library.

I also made a few other minor changes

• removed some of the blank dependency versions as they appeared to cause 'npm audit' to fail
• set the license field
• removed the bin/tester file and just put the command directly into package.json
• added the package-lock.json

Ran the unit tests and linter and they all passed.

[gareth-robinson]

Hmm, ok, not so easy as I hoped there. It works locally, but I'll see if I can work out what the travis issue is.

[gareth-robinson]

The latest version of thrift used a node method Buffer.alloc, which didn't exist before v5.10 so in changing the thrift version I also had to change the target 'engines' for this library to v6 and above - also changed the travis package to match.