make install assumes that Go binaries are installed in $GOPATH/bin - this is a bad assumption

### Subject of the issue

Go binaries are installed to $GOBIN if that env variable exists. Having $GOBIN set and pointing to a different location than $GOPATH/bin will cause `make install` to fail.

The solution is to check for the existence of the $GOBIN env variable and use that, or to explicitly state that this configuration is not supported.