[Rd] omission col as vector argument in hist documentation (PR#13722)

[astokes at esica.com]

Full_Name: Allan Stokes
Version: 2.8.1
OS: XP
Submission from: (NULL) (24.108.0.245)


Concerning the "col" argument, doc states only that col is "a colour to be used
to fill the bars. The default of NULL yields unfilled bars." 

It omits to mention that the col argument takes a vector which applies to the
bars in left to right order with recycling.