vlan group option name is 'vlan_group' not 'group' (#1138)

* Update netbox_vlan_module.rst

As per line 169 of https://github.com/netbox-community/ansible_modules/blob/devel/plugins/modules/netbox_vlan.py the name of the vlan group option is vlan_group not group

* Update netbox_vlan.py

As per line 37 and line 169 the option name for a VLAN group is vlan_group not group.

Author: vincemulhollon

docs/plugins/netbox_vlan_module.rst

@@ -796,7 +796,7 @@ Examples
               name: Test VLAN
               vid: 400
               site: Test Site
-              group: Test VLAN Group
+              vlan_group: Test VLAN Group
               tenant: Test Tenant
               status: Deprecated
               vlan_role: Test VLAN Role

plugins/modules/netbox_vlan.py

@@ -122,7 +122,7 @@
           name: Test VLAN
           vid: 400
           site: Test Site
-          group: Test VLAN Group
+          vlan_group: Test VLAN Group
           tenant: Test Tenant
           status: Deprecated
           vlan_role: Test VLAN Role