travis: Add more checks now that the bug is found
travis: Add more checks now that the bug is found

I found the issue: YAML hates colon ':' and this got in the way. I never found
the correct way to escape the colon so I replaced it with 'depends on'. This is
really sad as there's another colon in the command in the echo part and it is
parsed works fine. <shrug>.

I want to eventually add test coverage on both 1.7.6 (which includes t.Run())
and go1.5.4 (which is fairly old) but that requires learning more about travis
matrix or condition steps out.

google/periph