Use relative paths for exec and require

Don't assume that the current working directory is the same as the
directory where the script is located.

I'm not really sure how this worked without this change as the
current working directory for the make-deploy-notes invocation
needs to be the working directory of a mediawiki/core.git clone.

Change-Id: Ibd65eaae19236f620987df52545e060484a1ba29