fix matcher

Author: swissspidy

features/testing.feature

@@ -128,7 +128,7 @@ Feature: Test that WP-CLI loads.
   Scenario: Verify sys_get_temp_dir() in sub-process
     Given a WP install
     When I run `wp eval 'echo sys_get_temp_dir();'`
-    Then STDOUT should not be:
+    Then STDOUT should not contain:
     """
     C:\Windows
     """