Fix HTTP basic authentication header detection for cURL example

[jandillmann]

Unfortunately there is a bug in my previous pull request #108.

Headers in specs are written with a HTTP_ prefix (e.g. HTTP_AUTHORIZATION), and given without alteration to the Curl class (source).

When generating the API documentation, headers for Curl are set by ClientBase (source), which includes Headers which formats them nicely (e.g. "Authorization") (source).

Therefore the spec is green, but the generated documentation does not show the username and password as desired. This pull request changes one line to use a regular expression to detect the authorization header, either written as HTTP_AUTHORIZATION or Authorization.

[oestrich]

I probably should have caught that. Thanks for checking up on this.