Update README.md (pauldemarco#710)

Fix Flutter homepage and description

Author: mit-mit

README.md

@@ -9,7 +9,7 @@
 
 ## Introduction
 
-FlutterBlue is a bluetooth plugin for [Flutter](http://www.flutter.io), a new mobile SDK to help developers build modern apps for iOS and Android.
+FlutterBlue is a bluetooth plugin for [Flutter](https://flutter.dev), a new app SDK to help developers build modern multi-platform apps.
 
 ## Alpha version