Fixed capitalization

Author: vanillajonathan

README.markdown

@@ -18,7 +18,7 @@ RestSharp is in need of more maintainers.  Specifically ones who have more exper
 * Automatic detection of type of content returned
 * GET, POST, PUT, PATCH, HEAD, OPTIONS, DELETE supported
 * Other non-standard HTTP methods also supported
-* oAuth 1, oAuth 2, Basic, NTLM and Parameter-based Authenticators included
+* OAuth 1, OAuth 2, Basic, NTLM and Parameter-based Authenticators included
 * Supports custom authentication schemes via IAuthenticator
 * Multi-part form/file uploads
 * T4 Helper to generate C# classes from an XML document