vim: set modified-by to the recipe MAINTAINER

vim: set modified-by to the recipe MAINTAINER

Clause II.3 of the Vim license states that any distribution of Vim that
has been extended or modified must _at least_ indicate in the :version
output that this is the case.

Handily, Vim has a --with-modified-by argument to add a line in that
text, so use MAINTAINER.  This is the distribution maintainer contact,
by default it is OE-Core Developers
<openembedded-core@lists.openembedded.org>.

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>