Fix: apt-get update before travis CI install dependency

.travis.yml

@@ -12,6 +12,7 @@ script:
 after_success:
   - bash <(curl -s https://codecov.io/bash)
 before_deploy:
+  - sudo apt-get update
   - sudo apt-get -y install gcc-mingw-w64-x86-64
   - sudo apt-get -y install gcc-arm-linux-gnueabihf libc6-dev-armhf-cross
   - chmod +x ./build.sh