Update book.tex

Fixing a typo -- thanks, Bjorn!

Author: AllenDowney

book/book.tex

@@ -16902,7 +16902,7 @@ \section{Hashtables}
 {\tt BetterMap}: if they are equal, the average number of items per
 LinearMap is 1, so it calls {\tt resize}.
 
-{\tt resize} make a new {\tt BetterMap}, twice as big as the previous
+{\tt resize} makes a new {\tt BetterMap}, twice as big as the previous
 one, and then ``rehashes'' the items from the old map to the new.
 
 Rehashing is necessary because changing the number of LinearMaps