travis: check go vet and gofmt (go-sql-driver#577)

* travis: check go vet and gofmt

This makes the tests fail if go vet or gofmt find something

* travis: use gofmt simplify flag

Author: julienschmidt

.travis.yml

@@ -75,3 +75,7 @@ matrix:
 
 before_script:
   - mysql -e 'create database gotest;'
+script:
+  - go test -v
+  - go vet ./...
+  - test -z "$(gofmt -d -s . | tee /dev/stderr)"