Litle fixes

[DeadBryam]

This pull request fixes #73 and #72 issues.

And change "compile" to "implementation" for the newer versions of Gradle.

[cazmo99]

Can this be used without waiting for the merge request?

[xni06]

Can this be used without waiting for the merge request?

You can use something like this in your pubspec.yaml

  bluetooth_print:
    git:
      url: https://github.com/thon-ju/bluetooth_print.git
      ref: 1f15040f674b2f593f83b595cc2b9dc29569309e

[javieritis]

It's possible merge this changes?