remove \n from header

this is no longer valid HTTP 1.1 and node _http_outgoing will throw an exception like:

_http_outgoing.js:355
2016-05-07T17:08:01.538212+00:00 app[web.1]:       throw new TypeError('The header content contains invalid characters');

Author: kevinmarks

lib/twitter.js

@@ -146,7 +146,7 @@ OAuthParams.prototype.getHeader = function(){
         }
     }
     this.args = args;
-    return 'OAuth '+lines.join(',\n ');
+    return 'OAuth '+lines.join(', ');
 }