Fixup for LWG3079 LWG 2935 forgot to fix the existing_p overloads of create_directory

Author: jensmaurer

source/iostreams.tex

@@ -14812,7 +14812,7 @@
   directory \tcode{p} resolves to, with
   attributes copied from directory \tcode{existing_p}. The set of attributes
   copied is operating system dependent.
-  Creation failure because \tcode{p} already exists is not treated as an error.
+  Creation failure because \tcode{p} already exists is not an error.
 \begin{note} For POSIX-based operating systems, the
       attributes are those copied by native API \tcode{stat(existing_p.c_str(), \&attributes_stat)}
       followed by \tcode{mkdir(p.c_str(), attributes_stat.st_mode)}. For