Merge pull request #6194 from ghen2/hostname

Portability: use `uname -n` instead of `hostname`.

acme.sh

@@ -6813,7 +6813,7 @@ _send_notify() {
 
   _nsource="$NOTIFY_SOURCE"
   if [ -z "$_nsource" ]; then
-    _nsource="$(hostname)"
+    _nsource="$(uname -n)"
   fi
 
   _nsubject="$_nsubject by $_nsource"