libevent: Follow move to github

packages/libevent/build.sh

@@ -1,6 +1,6 @@
 TERMUX_PKG_HOMEPAGE=http://libevent.org/
 TERMUX_PKG_DESCRIPTION="Library that provides asynchronous event notification"
 TERMUX_PKG_VERSION=2.0.22
-TERMUX_PKG_SRCURL=http://downloads.sourceforge.net/project/levent/libevent/libevent-2.0/libevent-${TERMUX_PKG_VERSION}-stable.tar.gz
+TERMUX_PKG_SRCURL=https://github.com/libevent/libevent/releases/download/release-${TERMUX_PKG_VERSION}-stable/libevent-${TERMUX_PKG_VERSION}-stable.tar.gz
 # Strip away libevent core, extra and openssl libraries until someone uses them
 TERMUX_PKG_RM_AFTER_INSTALL="bin/event_rpcgen.py lib/libevent_*"