Restrict appveyor to master branch builds, and test dartdoc on OSX (#1736)

Author: jcollins-g

.travis.yml

@@ -10,6 +10,10 @@ env:
   - DARTDOC_BOT=sdk-docs
 script: ./tool/travis.sh
 
+os:
+  - osx
+  - linux
+
 branches:
   only: [master]
 cache:

appveyor.yml

@@ -2,6 +2,10 @@
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
+branches:
+  only:
+    - master
+
 install:
   - ps: wget https://storage.googleapis.com/dart-archive/channels/dev/raw/latest/sdk/dartsdk-windows-x64-release.zip -OutFile dart-sdk.zip
   - cmd: echo "Unzipping dart-sdk..."