Avoid ugly linewrap in git help

Avoid ugly linewrap in git help

Some of the short help texts that are shown e.g. when running 'git'
without any parameters wrap on a 80-column terminal.  They are just
one character over the line.  This patch avoids it by decreasing the
number of spaces around the preceding command name from four to
three (on both sides for symmetry).

Signed-off-by: Rene Scharfe <rene.scharfe@lsrfire.ath.cx>
Signed-off-by: Junio C Hamano <junkio@cox.net>