fix examples in collapse_branch

[jangorecki]

There is a call to library(ape) in collapse_branch.Rd examples. As the ape is suggested dependency, it should not be required to run examples according to R-exts. This can be conditionally escaped with requireNamespace. It is possible there are other cases of that issue in other examples, this one was to first that fails due to not having ape pkg.

[talgalili]

Thanks @jangorecki you are correct. I will fix this later on.

With regards, Tal

[jangorecki]

Similarly colorspace package in color_unique_labels examples. Regards, Jan

[talgalili]

Thanks, I'll make sure to fix it before the next release. :)