Use guide = "none" instead of guide = FALSE

[ndunnewind]

Using guide = FALSE has been deprecated since ggplot2 3.3.4.

A deprecation warning is shown when running e.g. the example in plot.nma_data:

af_net <- set_agd_arm(atrial_fibrillation,
                      study = studyc,
                      trt = abbreviate(trtc, minlength = 3),
                      r = r,
                      n = n,
                      trt_class = trt_class)
plot(af_net)

Warning message:
It is deprecated to specify `guide = FALSE` to remove a guide. Please use `guide = "none"` instead. 

[dmphillippo]

Thanks @ndunnewind, merging in for the next release