Travis: Run tests on Windows.

[dmitshur]

There has been work done to the library over time to support Windows. There's a chance for Windows support to deteriorate over time, since it's not tested often. Fix that by running tests on Windows in CI. Travis CI has recently added support for Windows, making this possible.

References:

• https://blog.travis-ci.com/2018-10-11-windows-early-release
• https://twitter.com/travisci/status/1050777251862720513

[dmitshur]

Looks like it'll take some work to get tests to pass on Windows. I see the following issues so far:

• gofmt reports every file as not formatted; this is likely because the line endings of .go files being checked out are converted to from \n to \r\n. This shouldn't be done.
  • A fix might be to configure the git repo (or tell Travis to) such that the .go files keep their canonical \n newlines when checked out on Windows. https://help.github.com/articles/dealing-with-line-endings/#platform-windows is related.
  • An alternative fix is to skip gofmt on Windows. I suspect this option is worse.
• On Go 1.11.1, ./vcs/... packages are failing because of exec: "gcc": executable file not found in %PATH%.
  • Not sure why this is happening in Go 1.11.1 build but not Go 1.9.7 build.
• On Go 1.9.7, gcc is not an issue and packages are building, but an SSH test in ./vcs fails because a key file fail to be deleted: Error removing SSH key file C:\Users\travis\AppData\Local\Temp\go-vcs-gitcmd-key385111935: remove C:\Users\travis\AppData\Local\Temp\go-vcs-gitcmd-key385111935: The process cannot access the file because it is being used by another process..
• On master, gimme fails to install Go.

[dmitshur]

Looks like @keegancsmith is seeing very similar issues in https://github.com/sourcegraph/go-langserver/pull/329, and has reported about them at:

• https://travis-ci.community/t/go-cant-find-gcc-with-go1-11-1-on-windows/293
• https://travis-ci.community/t/files-in-checkout-have-eol-changed-from-lf-to-crlf/349

This PR can wait until that's resolved.

[dmitshur]

This PR is probably obsolete since Travis CI has changed quite a bit over the years and there are newer alternatives available by now. It's a trivial 3 line change that can be re-recreated if needed. Closing.