couchbeam clone url on install

same as pull request 44 (@ddgenome makes a good point)
* in the far most cases port 9418 (git://) is blocked by the firewall
* some people give up on receiving the error message:
 <pre>
ERROR: git clone -n git://github.com/benoitc/couchbeam.git 
couchbeam failed with error: 128 and output:
fatal: unable to connect to github.com
</pre>
 so using `https://` lowers the threshold
* I do not think that `git://` is more reliable than `https://` in this case