pygrass: fix error message

git-svn-id: https://svn.osgeo.org/grass/grass/branches/releasebranch_7_0@60568 15284696-431f-4ddb-bdfa-cd5b030d7da7

lib/python/pygrass/modules/interface/module.py

@@ -368,7 +368,7 @@ class Module(object):
                 if ((k in self.inputs and self.inputs[k].value is None) or
                         (k in self.outputs and self.outputs[k].value is None)):
                     msg = "Required parameter <%s> not set."
-                    raise ParameterError(msg % key)
+                    raise ParameterError(msg % k)
             return self.run()