update pub.dev version to newest master

[BujusKrachus]

Currently the version 1.0.1 on pub.dev will not work with newer flutter versions or newer flutter packages in particular, due to the xml version, which got luckily bumped already in f78e785. Unfortunately this change is not yet on pub.dev, please update @biocarl if you find some time.

For other readers: Use this in your pubspec.yaml:

  drawing_animation:
    git:
      url: https://github.com/biocarl/drawing_animation.git
      ref: f78e785933774533d207c67d4f3728ee7ca4d8a6