install latest arduino on Mac (microsoft#724)

Author: czgtest

.travis.yml

@@ -38,9 +38,10 @@ before_install:
   fi
 # Arduino 1.8.7 has breaking change, Install board package and library will fail
 # https://github.com/arduino/Arduino/issues/8034
+# Arduino 1.8.8 has fixed issue 8034.
 - if [ $TRAVIS_OS_NAME == "osx" ]; then
     /usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)";
-    brew cask install https://raw.githubusercontent.com/Homebrew/homebrew-cask/f908f03d37c981de93af8447b32641551d8bf74e/Casks/arduino.rb;
+    brew cask install arduino;
   fi
 
 install: