Use upstream homebrew source

Change-Id: I962c533587845ec16fda16cf4e2075e84fbc550b
Reviewed-on: http://review.couchbase.org/24894
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>