`group_by_()` was deprecated in dplyr 0.7.0.

[kailesmith]

While using slide() I received the following notice:

Warning message: group_by_() was deprecated in dplyr 0.7.0. ℹ Please use group_by() instead. ℹ See vignette('programming') for more help ℹ The deprecated feature was likely used in the DataCombine package. Please report the issue at https://github.com/christophergandrud/DataCombine/issues. This warning is displayed once every 8 hours. Call lifecycle::last_lifecycle_warnings() to see where this warning was generated.