Ordering alphabetically dependencies.

[llrs]

I was about to open this issue in usethis, but I saw it used desc to manage the DESCCRIPTION file. Let me know if I missed and should be on usethis.

When I use devtools::setup packages are added alphabetically:

Suggests: 
    knitr,
    rmarkdown,
    testthat

However when using usethis::use_package or anything that adds a package to the DESCRIPTION file like use_coverage, the packages are added at the end of the list:

Suggests: 
    knitr,
    rmarkdown,
    testthat,
    covr

Could it be added an option in desc_normalizeto sort the packages alphabetically? Perhaps in desc_normalize and in desc_set_dep as an argument?.

Suggests: 
    covr,
    knitr,
    rmarkdown,
    testthat

[gaborcsardi]

I think it does not have be an option, desc_normalize should just do it. Do you want to submit a PR?

[llrs]

It was merged on #67