Bump es6-module-transpiler version to ~0.6

Bumps the transpiler version to 0.6 to keep dependencies up to date.
Output of `npm run test`:
```
npm run test

> gulp-es6-module-transpiler@0.1.1 test /Users/aesthaddicts/Development/gulp-es6-module-transpiler
> mocha


  ․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․

  40 passing (30ms)
```