Update default values to match 50/72 rule

The 50/72 rule was laid out by tpope in 2008 (see
www.tpope.net/node/106), and has gained wide acceptance
in the git community. It makes sense to enforce it by
default, since the values are configurable anyway.

Change-Id: I472ddbd2caf7cd1036f8ce2953380445bca8712a