[Rd] Unclosed parenthesis in grep.Rd

[Hugh Parsonage]

Lines 129-131:
\code{grep(value = FALSE)} returns a vector of the indices
of the elements of \code{x} that yielded a match (or not, for
\code{invert = TRUE}. This will be an integer vector unless the input

There should be a closing parenthesis after \code{invert = TRUE}