[Rd] minor doc bug: options.Rd should be updated

[Deepayan Sarkar]

src/library/base/man/options.Rd Currently has:

    \item{\code{expressions}:}{sets a limit on the number of nested
      expressions that will be evaluated.
      Valid values are 25\dots100000 with default 500.}

The last line should be 

      Valid values are 25\dots500000 with default 5000.}

-Deepayan