Go 1.9.4

[leonklingele]

• Have you followed the guidelines for contributing?
• Have you checked that there aren't other open pull requests for the same formula update/change?
• Have you built your formula locally with brew install --build-from-source <formula>, where <formula> is the name of the formula you're submitting?
• Does your build pass brew audit --strict <formula> (after doing brew install <formula>)?

[leonklingele]

This is a security release. See golang/go#23672

[ilovezfs]

Thanks @leonklingele!