Pull request "fix(docs): change to the new is_fitted() API" by @davydof from catboost/catboost#895

MERGED FROM catboost/catboost#895 Note: mandatory check (NEED_CHECK) was skipped ref:017f26ed807590374ad3d297c77d3321b6cb8d9e

Author: arcadia-devtools

ru/ml_session_2018_tutorial_ru.ipynb

@@ -351,7 +351,7 @@
  " eval_set=(X_validation, y_validation),\n",
  " logging_level='Silent'\n",
  ")\n",
- "print('Model is fitted: ' + str(model.is_fitted_))\n",
+ "print('Model is fitted: ' + str(model.is_fitted()))\n",
  "print('Model params:')\n",
  "print(model.get_params())"
  ]