Broken Go 1.7 and 1.8 builds

[nyanshak]

Travis CI builds fail because golint no longer supports Go 1.7 and 1.8. Technically 1.9 is no longer supported, but still works. See golint release policy.

Proposed fixes:

• Make Go-version-specific imports / pin golint version to support 1.7 and 1.8
• Drop 1.7 and 1.8 from builds

I propose following option 2 (drop 1.7 / 1.8). In addition, I suggest we follow the Go release policy and support only the last two major releases (1.10 and 1.11).

I'll raise a PR to change the builds based on the decision in this thread.

cc @zorkian / @yfronto

[ghost]

I'm okay dropping 1.7 and 1.8 from the tests.

[nyanshak]

191 merged to fix this