Modernize deprecated syntax in Behat tests (#338)

Author: schlessera

features/db-import.feature

@@ -147,7 +147,7 @@ Feature: Import a WordPress database
       wp db import
       """
 
-    When I run `wp core config {CORE_CONFIG_SETTINGS}`
+    When I run `wp config create {CORE_CONFIG_SETTINGS}`
     Then STDOUT should not be empty
     And the wp-config.php file should exist