add package year in knitcitation's DESCRIPTION file

[hpiwowar]

It'll help us cite the knitcitation package properly when we're using author-date format. Thanks :)

[cboettig]

Hehe, I've filed an identical issue in Hadley's repo once upon a time. CRAN adds publication date automatically to the description file when the package is released, e.g. http://cran.r-project.org/web/packages/knitcitations/index.html so it's easiest not to have a date in the file. Like you observe, it means that anyone using the development/github version of the package cannot cite the thing properly. Adding now.

[hpiwowar]

yay, thanks Carl! That was way faster than I could implement a workaround :)