www-plugins/browserpass: Install to both firefox dirs

www-plugins/browserpass: Install to both firefox dirs

Firefox's directory for native messaging hosts is a compile-time
variable. www-client/firefox-bin is set to a directory under /usr/lib/,
while www-client/firefox varies. This -r2 bump will install to both
locations so that both firefox and firefox-bin are able to locate the
plugin.

Bug: https://bugs.gentoo.org/687746
Closes: https://github.com/gentoo/gentoo/pull/14643
Signed-off-by: Lucian Poston <lucianposton@pm.me>
Signed-off-by: Matt Turner <mattst88@gentoo.org>