conditional apt-get

.travis.yml

@@ -7,7 +7,7 @@ os:
   - osx
 sudo: true
 before_script:
-  - sudo apt-get install gcc-multilib g++-multilib 
+  - if [[ "$TRAVIS_OS_NAME" == "linux" ]]; then sudo apt-get install gcc-multilib g++-multilib; fi
 script:
   - mkdir -p build && cd build
   - cmake ../ -DCMAKE_EXE_LINKER_FLAGS="-Wl,--no-undefined" -DUSE_VOICEMGR=0 && make -j3 && rm -rf *