Bug 942219 - Wrong homebrew url in bootstrap-mac.sh

See Bug 942219 - Wrong homebrew url in bootstrap-mac.sh:

The bootstrap script for mac points to:
        https://raw.github.com/mxcl/homebrew/go
for auto-downloading homebrew.

This should be here:
        https://raw.github.com/mxcl/homebrew/go/install

This commit corrects the url.