Misspelled `language: minmal` doesn't fail

Setting invalid value for a language doesn’t fail the build.

language: minmal

This makes initial setup of Travis harder than alternative CI.

https://travis-ci.com/yakshaveinc/travis/jobs/178155333

@BanzaiMan if it is not a bug, then how to mark this as an user issue? Maybe you can move it into appropriate category?

Imprint