Depend on develop branch of ekka

Makefile

@@ -9,7 +9,7 @@ dep_gproc        = git https://github.com/uwiger/gproc
 dep_getopt       = git https://github.com/jcomellas/getopt v0.8.2
 dep_lager        = git https://github.com/basho/lager master
 dep_esockd       = git https://github.com/emqtt/esockd master
-dep_ekka         = git https://github.com/emqtt/ekka emq24
+dep_ekka         = git https://github.com/emqtt/ekka develop
 dep_mochiweb     = git https://github.com/emqtt/mochiweb master
 dep_pbkdf2       = git https://github.com/emqtt/pbkdf2 2.0.1
 dep_lager_syslog = git https://github.com/basho/lager_syslog