Example is deprecated

[ekothe]

https://github.com/djnavarro/rbook/blob/8aeeb95ba8729f6e4239033505c8449556490c29/bookdown/02.04-mechanics.Rmd#L859

According to the PDF version this should result in

> print.formula( my.formula ) # print it out using the print.formula() method 
blah ~ blah.blah

However the when evaluated this actually returns

print.formula( my.formula )       # print it out using the print.formula() method

## Appears to be deprecated

An example using a non-deprecated generic should be used to replace this

[Maschette]

print.formula is an alias for formula() but it is still there and just not exported for some reason. ``

stats:::print.formula(my.formula) blah ~ blah.blah ``