unity8/mir: bump pkgrel after soname bump

Increase 'mir' pkgrel (2 -> 3), missing depend(s): so:libnettle.so.6

[ci:skip-build]: won't finish in time

unity8/mir/APKBUILD

@@ -2,7 +2,7 @@
 # Maintainer: Luca Weiss <luca@z3ntu.xyz>
 pkgname=mir
 pkgver=1.1.2
-pkgrel=2
+pkgrel=3
 pkgdesc="Canonical's display server"
 url="https://mir-server.io"
 arch="x86_64"