Add 'lager_syslog' dependency

rebar.config

@@ -1,4 +1,4 @@
 {deps, [
-{gproc,".*",{git,"https://github.com/uwiger/gproc",""}},{lager,".*",{git,"https://github.com/basho/lager","master"}},{esockd,".*",{git,"https://github.com/emqtt/esockd","master"}},{mochiweb,".*",{git,"https://github.com/emqtt/mochiweb",""}}
+{gproc,".*",{git,"https://github.com/uwiger/gproc",""}},{lager,".*",{git,"https://github.com/basho/lager","master"}},{esockd,".*",{git,"https://github.com/emqtt/esockd","master"}},{mochiweb,".*",{git,"https://github.com/emqtt/mochiweb",""}},{lager_syslog,".*",{git,"https://github.com/basho/lager_syslog",""}}
 ]}.
 {erl_opts, [{parse_transform,lager_transform}]}.