Update ranch to 1.3.1 in rebar.config

Update to match the Makefile change in 3a240eb49b6322ec88985aa21014ca84a81157bb. Fixes #1088

rebar.config

@@ -1,2 +1,2 @@
-{deps, [{cowlib,".*",{git,"https://github.com/ninenines/cowlib","1.0.2"}},{ranch,".*",{git,"https://github.com/ninenines/ranch","1.2.0"}}]}.
+{deps, [{cowlib,".*",{git,"https://github.com/ninenines/cowlib","1.0.2"}},{ranch,".*",{git,"https://github.com/ninenines/ranch","1.3.1"}}]}.
 {erl_opts, [debug_info,warn_export_all,warn_export_vars,warn_shadow_vars,warn_obsolete_guard,warn_missing_spec]}.