Add proper type to path and link

Since both of them are path, it should be checked using the
proper type.

lib/ansible/modules/extras/system/alternatives.py

@@ -67,8 +67,8 @@ def main():
     module = AnsibleModule(
         argument_spec = dict(
             name = dict(required=True),
-            path = dict(required=True),
+            path = dict(required=True, type='path'),
-            link = dict(required=False),
+            link = dict(required=False, type='path'),
         ),
         supports_check_mode=True,
     )