Don't treat `...` as an "identifier with dots"

[krlmlr]

-## R/summarise.r:38:67: style: Words within variable and function names should be separated by '_' rather than '.'.
-##     names <- unname(unlist(lapply(match.call(expand.dots = FALSE)$`...`, deparse)))
-##                                                                   ^~~~~

[fangly]

I think this was fixed a while ago. In any case, I checked that the behavior was correct in #214 .