Update .travis.yml in accordance with goveralls document
Update .travis.yml in accordance with goveralls document

https://github.com/mattn/goveralls#travis-ci

pawmart/api2go-gin-gorm,hnakamur/api2go-gorm-gin-crud-example,pawmart/api2go-gin-gorm,hnakamur/api2go-gorm-gin-crud-example