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

diff --git a/.travis.yml b/.travis.yml
index ba30510..3f0c780 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -10,6 +10,10 @@
   - DARTDOC_BOT=sdk-docs
 script: ./tool/travis.sh
 
+os:
+  - osx
+  - linux
+
 branches:
   only: [master]
 cache:
diff --git a/appveyor.yml b/appveyor.yml
index 252bdf4..ef3b203 100644
--- a/appveyor.yml
+++ b/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..."