[Rd] typo in R-lang.texi

[Stephen Eglen]

Hi, 

R-lang.texi line 2020/1 currently says:

  This allows, e.g., a 
  local variable in a function to have the same name AS a global object. 

The word "AS" is missing in that sentence.

(Line number according to
 https://svn.r-project.org/R/trunk/doc/manual/R-lang.texi)

Stephen