[now-go] Update go to version 1.13.7 (#3750)
[now-go] Update go to version 1.13.7 (#3750)

Updates go to the latest version 1.13.7 (https://golang.org/doc/devel/release.html#go1.13). This allows users to use the new error functionality that was introduced in go 1.13 (https://blog.golang.org/go1.13-errors) and also includes a couple of security fixes.

Looking at the last PR that updated the version (https://github.com/zeit/now-builders/pull/247/files) this should be as simple as updating the version number.

P.S. I tried to follow the contribution guidelines, but `yarn lint` fails with `exit code 1`/`295 problems (33 errors, 262 warnings)` and `yarn test` returns `error Command "test" not found` on master. But `yarn test-unit` shows no errors.
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