Update URL in AVR installation notes

[Marek Michalkiewicz]

Hello,

I've just noticed an outdated URL to my small AVR archive...

Please change the URL <http://www.itnet.pl/amelektr/avr>
to <http://www.amelek.gda.pl/avr/>
in the the document <http://gcc.gnu.org/install/specific.html>.

There is a permanent redirect from the first to the second URL, but it
may disappear at any time (as I no longer use that ISP).  In general,
if you see any other URL starting with <http://www.itnet.pl/amelektr>,
please change it to start with <http://www.amelek.gda.pl> instead.
Thanks!

Marek