Download and install go before running tests

.gitlab-ci.yml

+before_script:
+  - rm -rf /usr/local/go
+  - apt-get install -y curl
+  - curl -O https://storage.googleapis.com/golang/go1.5.1.linux-amd64.tar.gz
+  - echo '46eecd290d8803887dec718c691cc243f2175fe0  go1.5.1.linux-amd64.tar.gz' | shasum -c -
+  - tar -C /usr/local -xzf go1.5.1.linux-amd64.tar.gz
+  - export PATH=/usr/local/go/bin:$PATH
+
 test:
   script: make clean test