Skip `go fmt` CI check for Go 1.8

`go fmt ./...` affects the `vendor/` directory before Go 1.9.

script/test

@@ -37,7 +37,7 @@ go test ./... || STATUS="$?"
 script/ruby-test "$@" || STATUS="$?"
 [ -z "$HUB_COVERAGE" ] || script/coverage summarize "$min_coverage" || STATUS=1
 
-if [ -n "$CI" ]; then
+if [ -n "$CI" ] && [[ "$(go version)" != *" go1.8."* ]]; then
   make fmt >/dev/null
   if ! git diff -U1 --exit-code; then
     STATUS=1