Updated rebar to latest master

rebar.config

@@ -2,9 +2,8 @@
     {proper, ".*", {git, "https://github.com/manopapad/proper.git", "master"}}
 ]}.
 
+{port_specs, [{"priv/jiffy.so", ["c_src/*.c"]}]}.
 
-{port_sources, ["c_src/*.c"]}.
-{so_name, "jiffy.so"}.
 {port_envs, [
     %% Link the spidermonkey library
     {".*", "CFLAGS", "$CFLAGS -g -Wall"},