Manual pages: rename EXAMPLE section to EXAMPLES

Manual pages: rename EXAMPLE section to EXAMPLES

Earlier, I patched various pages to consistently use EXAMPLE as a
section heading, rather than EXAMPLES.  (At that time, both headings
occurred in util-linux, with roughly equal frequency.)

Since then, I've observed that EXAMPLES is the more common usage
across a large corpus of manual pages. So, in Linux the man-pages
project, I switched to using EXAMPLES also. This patch makes the same
change for util-linux.

Signed-off-by: Michael Kerrisk (man-pages) <mtk.manpages@gmail.com>