fix before_script condition

Author: PeterIvanov

.travis.yml

@@ -1,6 +1,6 @@
 language: go
 
-before_script: [[ $TRAVIS_GO_VERSION =~ (^1\.8) ]]; then cd $GOPATH/src/github.com/stretchr/testify/ && git checkout v1.2.2 && cd -; fi
+before_script: if [[ $TRAVIS_GO_VERSION =~ (^1\.8) ]]; then cd $GOPATH/src/github.com/stretchr/testify/ && git checkout v1.2.2 && cd -; fi
 
 go:
   - "1.8.x"