Upgrade the esockd library to v5.2

Makefile

@@ -8,7 +8,7 @@ dep_goldrush     = git https://github.com/basho/goldrush 0.1.9
 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 develop
+dep_esockd       = git https://github.com/emqtt/esockd v5.2
 dep_ekka         = git https://github.com/emqtt/ekka master
 dep_mochiweb     = git https://github.com/emqtt/mochiweb develop
 dep_pbkdf2       = git https://github.com/emqtt/pbkdf2 2.0.1