fix spelling

Author: vladak

intro.tex

@@ -1176,7 +1176,7 @@
 \item Using a double \texttt{\$} suppresses the special meaning of a dollar
 sign, see the next slide.
 \item A character \texttt{@} at the beginning of a line suppresses its printout.
-Otherwise, \texttt{make} always prints out what is gonna be executed next.
+Otherwise, \texttt{make} always prints out what is going to be executed next.
 \item For a dry run, i.e. to see what would be executed, but do not execute
 anything, use option \texttt{-n}.
 \item A character \texttt{-} at the beginning of a line causes \texttt{make} to