Update appveyor.yml

Upgrade to the 1.10.0 SDK on the windows bot.
diff --git a/appveyor.yml b/appveyor.yml
index 4807cbb..c883701 100644
--- a/appveyor.yml
+++ b/appveyor.yml
@@ -3,7 +3,7 @@
 # BSD-style license that can be found in the LICENSE file.
 
 install:
-  - cinst -y dart-sdk
+  - cinst -y "Dart SDK"
   - set PATH=%PATH%;C:\tools\dart-sdk\bin
   - set PATH=%PATH%;%APPDATA%\Pub\Cache\bin
   - pub get