`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.