Add gatling 3.3.1, run as uid 1000, gid 1000 (#27)

[yayayahei]

At GoCD pipeline, it will run git clean -dffx firstly. But perviously gatilng image run as root user, it will cause Error when git clean repo.

[Greeff]

Just a suggestion, as part adding the latest Gatling, it would also be great if we could bump the scala version too.