Upgrade erlang-oauth to 1.5.0
Convert options to string instead of char list

From erlang-oauth version 1.5 or lator,
it accepts binary string as parameter.

And also we can use non-ascii in parameter.

see also
https://github.com/tim/erlang-oauth/issues/22
Merge pull request #1 from niku/options-convert-to-binary

Convert params to string instead of char list