Use PayPal.me instead of donation link

PayPal.me looks nicer.
Also make the button blue so it is more flashy.

See #15

Author: maoberlehner

README.md

@@ -1,5 +1,5 @@
 # vuex-map-fields
-[![Donate](https://img.shields.io/badge/Donate-PayPal-green.svg)](https://www.paypal.com/cgi-bin/webscr?cmd=_s-xclick&hosted_button_id=N8DK47KJLEAN8)
+[![Donate](https://img.shields.io/badge/Donate-PayPal-blue.svg)](https://paypal.me/maoberlehner)
 [![Build Status](https://travis-ci.org/maoberlehner/vuex-map-fields.svg?branch=master)](https://travis-ci.org/maoberlehner/vuex-map-fields)
 [![Coverage Status](https://coveralls.io/repos/github/maoberlehner/vuex-map-fields/badge.svg?branch=master)](https://coveralls.io/github/maoberlehner/vuex-map-fields?branch=master)
 [![GitHub stars](https://img.shields.io/github/stars/maoberlehner/vuex-map-fields.svg?style=social&label=Star)](https://github.com/maoberlehner/vuex-map-fields)