[travis] various fixes (#1601)

* various fixes

* disable code-signing on 'develop'

* fix yarn on xcode8 image

* rectify if statement

* comments

* improvement

.travis.yml

@@ -4,17 +4,17 @@ sudo: required
 branches:
   only:
     - develop
-    - travis
+    - master
 
 matrix:
   include:
 
     # WINDOWS cross-built from linux
     - os: linux
       dist: trusty
+      node_js: 6
       env:
           - GULP_PLATFORM=win
-      node_js: 6
       addons:
         apt:
           packages:
@@ -35,9 +35,9 @@ matrix:
     # LINUX
     - os: linux
       dist: trusty
+      node_js: 6
       env:
           - GULP_PLATFORM=linux
-      node_js: 6
       addons:
         apt:
           packages:
@@ -49,29 +49,23 @@ matrix:
 
     # MAC
     - os: osx
-      osx_image: xcode8.1
+      osx_image: xcode8  # currently xcode8.1+ doesn't support electron-builder macOS code-signing (https://github.com/electron-userland/electron-builder/issues/820#issuecomment-267777060)
+      node_js: 6
       env:
           - GULP_PLATFORM=mac
-      node_js: 6
       before_install:
-        - brew update
-        - brew install gnu-tar libicns graphicsmagick xz
-        - npm install -g gulp yarn
+          - npm install -g yarn  # macOS xcode8 image doesn't natively support yarn yet
 
 cache:
   yarn: true
-  directories:
-    - node_modules
-    - app/node_modules
-    - $HOME/.electron
-    - $HOME/.cache
 
 install:
   - PATH=$PATH:$HOME/.meteor && curl -L https://github.com/arunoda/travis-ci-meteor-packages/master/configure.sh | /bin/sh
-  - npm install -g meteor-build-client electron@1.3.5
+  - yarn global add gulp-cli meteor-build-client electron@1.3.5
   - yarn
 
 script:
+  - if [[ $TRAVIS_BRANCH != "master" ]]; then unset CSC_LINK CSC_KEY_PASSWORD; fi  # disable macOS code-signing (production certificate) on develop branch
   - travis_wait 60 gulp mist --platform $GULP_PLATFORM
 
 after_success: