added required missing field for common yaml fmt

lib/ansible/plugins/inventory/nmap.py

@@ -17,6 +17,10 @@ DOCUMENTATION = '''
     requirements:
       - nmap CLI installed
     options:
+        plugin:
+            description: token that ensures this is a source file for the 'nmap' plugin.
+            required: True
+            choices: ['nmap']
         address:
             description: Network IP or range of IPs to scan, you can use a simple range (10.2.2.15-25) or CIDR notation.
             required: True