Fix zip error when installing update from a private BitBucket repository.

The code that updates the OAuth signature didn't account for the fact that the oauth_signature query parameter would end up in the wrong place. Instead of being sorted alphabetically with the rest of parameters, it must be the *last* one.

Puc/v4/OAuthSignature.php

@@ -45,6 +45,7 @@ if ( !class_exists('Puc_v4_OAuthSignature', false) ):
 					'oauth_version' => '1.0',
 				)
 			);
+			unset($parameters['oauth_signature']);
 
 			//Parameters must be sorted alphabetically before signing.
 			ksort($parameters);