[pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

econml/dowhy.py

@@ -240,7 +240,7 @@ def __getattr__(self, attr):
             if attr in dir(self):
                 return getattr(self, attr)
             else:
-                raise AttributeError(f"call `DoWhyWrapper.fit` first before any other operations.")
+                raise AttributeError("call `DoWhyWrapper.fit` first before any other operations.")
         elif attr.startswith('dowhy__'):
             return getattr(self.dowhy_, attr[len('dowhy__'):])
         elif hasattr(self.estimate_._estimator_object, attr):