use https for doc links

port changes from the readme

Author: benoitc

rebar.config

@@ -24,6 +24,6 @@
                                  {packages, false},
                                  {subpackages, true},
                                  {top_level_readme,
-                                  {"./README.md", "http://github.com/benoitc/erlang-nat"}}]}]}
+                                  {"./README.md", "https://github.com/benoitc/erlang-nat"}}]}]}
            ]}.