Fix small typo

Author: abrahimladha

content/lambda-calculus/introduction/computable-lambda.tex

@@ -15,7 +15,7 @@
 \end{thm}
 
 \begin{proof}
-Wwe need to show that every partial computable function~$f$ is
+We need to show that every partial computable function~$f$ is
 !!{lambda defined} by a lambda term~$F$. By Kleene's normal form
 theorem, it suffices to show that every primitive recursive function
 is !!{lambda defined} by a lambda term, and then that the functions