remove extra comma

Author: vladak

intro.tex

@@ -131,7 +131,7 @@
 \item The above list is a tiny fraction of the whole Unix world.  Every
 proprietary Unix variant likely came from either UNIX~V or BSD, and added its
 own features.  This resulted in quite a few standards as well, see page
-\pageref{UNIXSTANDARDS}.  In the end vendors, agreed upon a small set of those.
+\pageref{UNIXSTANDARDS}.  In the end vendors agreed upon a small set of those.
 \item If you are interested in a detailed and up-to-date Unix system version
 history, go check \url{https://www.levenez.com/unix/}.
 \end{itemize}