Bug 15592 - spelling mistake in ~/Koha/koha-tmpl/intranet-tmpl/p./plugins/plugins...

Bug 15592 - spelling mistake in ~/Koha/koha-tmpl/intranet-tmpl/p./plugins/plugins-upload.tt

To Test:

checkthat "extention" has been changed to "extension" on line 27

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Brendan A Gallagher <brendan@bywatersolutions.com>
(cherry picked from commit 70086f1681155d8e63c9ee1b149c3f812df8f125)
Signed-off-by: Julian Maurice <julian.maurice@biblibre.com>
(cherry picked from commit 841aa118e575470af73ef3160c63a421b6d99b58)
Signed-off-by: Frédéric Demians <f.demians@tamil.fr>