Fix typo in stacks-morphisms

Thanks to Andrea
http://stacks.math.columbia.edu/tag/0CL9#comment-2449

stacks-morphisms.tex

@@ -7571,7 +7571,7 @@ \section{Valuative criteria}
 }
 $$
 where no dotted arrow exists with $A = \mathbf{C}[[t]]$ and
-$K = \mathbf{C}((t))$. Namely, the top vertical arrow is given
+$K = \mathbf{C}((t))$. Namely, the top horizontal arrow is given
 by a $G$-torsor over the spectrum of $K = \mathbf{C}((t))$. Since any $G$-torsor
 over the strictly henselian local ring $A = \mathbf{C}[[t]]$ is trivial, we see
 that if a dotted arrow always exists, then every $G$-torsor over