Update texdoc.tex

Fix typo: exist for exit

doc/texdoc.tex

@@ -165,7 +165,7 @@ \subsection{Command-line options}
 \begin{clopt}{\sopt{l}, \lopt{list}}
 Set \ci{mode} to |list|. Texdoc will show the lists of all relevant documents
 it found and ask you which to open. When used with the \lopt{nointeract}
-option, Texdoc will just show the lists of documents and exist successfully.
+option, Texdoc will just show the lists of documents and exit successfully.
 \end{clopt}
 
 \begin{clopt}{\sopt{m}, \lopt{mixed}}