Update intro_inventory.rst

<!--- I think a colon is missing-->

+label: docsite_pr

docs/docsite/rst/user_guide/intro_inventory.rst

@@ -322,7 +322,7 @@ Starting in Ansible version 2.4, users can use the group variable ``ansible_grou
     a_group:
         testvar: a
         ansible_group_priority: 10
-    b_group
+    b_group：
         testvar: b
 
 In this example, if both groups have the same priority, the result would normally have been ``testvar == b``, but since we are giving the ``a_group`` a higher priority the result will be ``testvar == a``.