travis: fix build process

[kortschak]

We have been seeing no-output time outs for OpenBLAS recently. This is an attempt to mitigate that.

During looking at the process I noticed that we don't seem to output the OpenBLAS sha1 anymore, the second commit restores that behaviour.

Finally, it appears that travis-ci have changed how they are shelling things and setting CGO_LDFLAGS only once at the site of install does not impact on the env of the go test invocation, so it is added there in the third commit.

Please take a look.

[kortschak]

For some reason that I don't understand the allow_failures is not working for this repo; the master branch should appear in a separate section of the travis build page (this is what happens for gonum/gonum). I cannot see any difference between the two repos in this section of .travis.yml.

Resolved. There were two matrix: stanzas and that is not OK.

[kortschak]

I don't really understand why we are installing CBLAS from netlib when we build OpenBLAS, but I'm going to leave that for another PR.

[vladimir-ch]

We should also update the README (it still uses github.com at one place, references cgo package, ...).

[kortschak]

I'll make those changes in the next PR.