double encoding when using PLAINTEXT

[jrauch]

LIne 20 in oauth/signature/plaintext.rb causes a double-encoding of the secret - resulting in the & being encoded to %2526 - breaking plaintext signatures.

[quirkey]

Hey jrauch

This was actually fixed already in the canonical repo:
http://github.com/oauth/oauth-ruby/commit/b80a57f73070f2bca58b0b3d5343bc7e1d811980

If you have any more issues/bugs please file them at oauth/oauth-ruby.
Thanks!