fix a typo in Chapter ends and coends

src/content/3.10/ends-and-coends.tex

@@ -2,7 +2,7 @@
 
 \lettrine[lhang=0.17]{T}{here are many intuitions} that we may attach to morphisms in a category,
 but we can all agree that if there is a morphism from the object
-$a$ to the object $b$ than the two objects are in some way
+$a$ to the object $b$ then the two objects are in some way
 ``related.'' A morphism is, in a sense, the proof of this relation. This
 is clearly visible in any poset category, where a morphism \emph{is} a
 relation. In general, there may be many ``proofs'' of the same relation