Trying using Gimme to switch Golang version

.travis.yml

@@ -55,6 +55,7 @@ before_install:
     fi
   - if [ $TRAVIS_BRANCH != 'develop' ] && [ $TRAVIS_PHP_VERSION == "5.6" ] && [ $TRAVIS_PULL_REQUEST == "false" ]; then
         export TRAVIS_TAG=$(curl --fail --user "${GH_API_USER}" -s https://api.github.com/repos/getgrav/grav/releases/latest | grep tag_name | head -n 1 | cut -d '"' -f 4);
+        eval "$(curl -sL https://raw.githubusercontent.com/travis-ci/gimme/master/gimme | GIMME_GO_VERSION=1.8 bash)";
         go get github.com/aktau/github-release;
         git clone --quiet --depth=50 --branch=master https://${BB_TOKEN}bitbucket.org/rockettheme/grav-devtools.git $RT_DEVTOOLS  &>/dev/null;
         if [ ! -z "$TRAVIS_TAG" ]; then