update flutter code example

Example 1: update flutter

flutter upgrade

Example 2: flutter update

$ flutter channel

Example 3: update flutter version

I want to upgrade most latest version. So I used below commands:

flutter channel dev

Flutter has 4 project branches / channels ie stable, master, dev, beta. First 
when we install it. flutter install stable channel. If you want to switch :

flutter channel chanel_name

Then donwload that :

flutter upgrade

Example 4: flutter change to beta channel to dev

$ flutter upgrade

Flutter 0.5.1 • channel beta • https://github.com/flutter/flutter.git
Framework • revision c7ea3ca377 (9 weeks ago) • 2018-05-29 21:07:33 +0200
Engine • revision 1ed25ca7b7
Tools • Dart 2.0.0-dev.58.0.flutter-f981f09760