Use travis qemu addon instead of calling brew manually

Author: phil-opp

.travis.yml

@@ -19,9 +19,11 @@ addons:
   apt:
     packages:
       - qemu-system-x86
+  homebrew:
+    packages:
+      - qemu
 
 install:
-  - if [ $TRAVIS_OS_NAME = osx ]; then brew update; brew install qemu; fi
   - if [ $TRAVIS_OS_NAME = windows ]; then choco install qemu; export PATH="/c/Program Files/qemu:$PATH"; fi
 
 before_script: