bump to latest supported version of SDK for windows

Closes #790

LGTM given by: @devoncarew

Squashed commit of the following:

commit df9837d
Author: Seth Ladd <sethladd@google.com>
Date:   Fri Aug 7 13:03:00 2015 -0700

    bump to latest supported version of SDK for windows

Author: sethladd

appveyor.yml

@@ -4,7 +4,7 @@
 
 install:
   # Investigate scoop?
-  - choco install -y dart-sdk -version 1.11.0
+  - choco install -y dart-sdk -version 1.11.1
   - set PATH=%PATH%;C:\tools\dart-sdk\bin
   - set PATH=%PATH%;%APPDATA%\Pub\Cache\bin
   - pub get