Log datetime at each execution

Somehow, procmail as installed on EL7 doesn't offer a way to log the
beginning of each execution.

Signed-off-by: Konstantin Ryabitsev <konstantin@linuxfoundation.org>
diff --git a/common.rc b/common.rc
index b183509..6fd8930 100644
--- a/common.rc
+++ b/common.rc
@@ -2,5 +2,6 @@
 COMSAT=no
 LOGFILE=/var/log/grokmirror/procmail.log
 PARSEMAIL=/usr/local/bin/parsemail.sh
+LOG="---`date -R`---"
 
 # vim: ts=2 sw=2 sts=2 et syntax=procmail