[Rd] Small typo in german translation

[Rainer Hurling]

Dear developers,

I found a small typo in the german translation for the aggregate() function:

In the string "keine Zeile für die Aggragation" it should be spelled 
'Aggregation' instead of 'Aggragation' (e instead a).

After a quick look into the sources, I found two places for it:

#grep -r -e "Aggragation" *
src/library/stats/po/R-de.po:msgstr "keine Zeile für die Aggragation"
Binary file src/library/translations/inst/de/LC_MESSAGES/R-stats.mo matches

This is (at least) on R-devel, I did not look into other versions. Hope, 
it is ok to not offer a diff for it.

Thanks for all your work.

Best regards,
Rainer Hurling