fix typo

Author: vladak

proc.tex

@@ -123,7 +123,7 @@
 \end{slide}
 
 \begin{itemize}
-\item A process will enter a kernel model either by a
+\item A process will enter a kernel mode either by a
 \emph{trap induced by the CPU} (page fault, unknown instruction, etc.)
 \emph{timer} (to invoke scheduler), \emph{interrupt} from a peripheral device,
 or synchronous trap (a standard library uses it to hand over the control to