removing the slightest typo

[iamYannC]

this is so small but really annoyed me when i read the documentation. sorry

[cregouby]

Hello @iamYannC

Thanks for this contribution, every bit counts ! The documentation shall not be edited manually as it is made from the roxygen2 paragraph in the source code : https://github.com/cregouby/luz/blob/da93f6a46583836e9040df700ae0b7496a87ebf8/R/callbacks-monitor-metrics.R#L53-L55 I've proposed a patch in your branch for that : https://github.com/iamYannC/luz/pull/1

[dfalbel]

Will be fixed in #155