Support version flag when getting with `go get github.com/danielgtaylor/apisprout`

[momotaro98]

Thank you for creating this great tool.

I would like to see version of apisprout when I get it with go get github.com/danielgtaylor/apisprout .

Currently, I got Error: unknown flag: --version since a binary from go get isn't generated from govvv build in release.sh

Step to encounter the unkown flag error.

$ go get github.com/danielgtaylor/apisprout
$ which apisprout
/my-GOPATH/go/bin/apisprout
$ apisprout --version
Error: unknown flag: --version
Usage:
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.
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