modules: use GitHub mirror

Then using GitHub actions, the OpenWrt Git service occasinally returns a 504 leading to a failed build.

modules: use GitHub mirror
b427a3b1 · David Bauer · Martin Weinelt · ebac7e44 · b427a3b1
Commit b427a3b1 authored Mar 29, 2020 by David Bauer Committed by Martin Weinelt Apr 4, 2020
--- a/modules
+++ b/modules
 GLUON_FEEDS='packages routing gluon'

-OPENWRT_REPO=https://git.openwrt.org/openwrt/openwrt.git
+OPENWRT_REPO=https://github.com/openwrt/openwrt.git
 OPENWRT_BRANCH=openwrt-19.07
 OPENWRT_COMMIT=81264ebb51991aa2d17489852854e3b5ec3f514d