Make AppVeyor run pub get for the test package as well to regenerate .packages

Author: jcollins-g

appveyor.yml

@@ -9,6 +9,11 @@ install:
   - set PATH=%PATH%;C:\tools\dart-sdk\bin
   - set PATH=%PATH%;%APPDATA%\Pub\Cache\bin
   - pub get
+  - cmd: cd testing
+  - cmd: cd test_package
+  - cmd: pub get
+  - cmd: cd ..
+  - cmd: cd ..
 
 build: off