Add Go tip to coverage matrix

[kevinburke]

intriguingly, looks like there are failures on tip.

    dump_test.go:988: Dump #204

         got: ([6]testdata._Ctype_uchar) (len=6 cap=6) {

         00000000  74 65 73 74 35 00                                 |test5.|

        }

         want: ([6]testdata._Ctype_uint8_t) (len=6 cap=6) {

         00000000  74 65 73 74 35 00                                 |test5.|

        }

    dump_test.go:988: Dump #205

         got: ([6]testdata._Ctype_uchar) (len=6 cap=6) {

         00000000  74 65 73 74 36 00                                 |test6.|

        }

         want: ([6]testdata._Ctype_custom_uchar_t) (len=6 cap=6) {

         00000000  74 65 73 74 36 00                                 |test6.|

        }

[dmitshur]

intriguingly, looks like there are failures on tip.

Looks like Cgo-related changes that spew will need to take into account for Go 1.10.

Meanwhile, you can make tip failure an allowed failure (with fast finish):

matrix:
  allow_failures:
    - go: master
  fast_finish: true

See here for an example .travis.yml.

[davecgh]

I've merged the necessary changes to the tests so they work with the latest Go tip to master. Please update this per the review and I'll get it merged.

[kevinburke]

please rename the PR title to reflect reality

Ah, I amended the commit, but the PR title doesn't update when that happens, which is a little annoying. This should be ready for review again.