Add missing pushforward

Thanks to Dario Weissmann
https://stacks.math.columbia.edu/tag/01R8#comment-4285

morphisms.tex

@@ -880,7 +880,7 @@ \section{Scheme theoretic image}
 X' = \coprod U_i \longrightarrow X \longrightarrow Y.
 $$
 Then $f_*\mathcal{O}_X$ is a subsheaf of $f'_*\mathcal{O}_{X'}$,
-and hence $\mathcal{I} = \Ker(\mathcal{O}_Y \to \mathcal{O}_{X'})$.
+and hence $\mathcal{I} = \Ker(\mathcal{O}_Y \to f'_*\mathcal{O}_{X'})$.
 By Schemes, Lemma \ref{schemes-lemma-push-forward-quasi-coherent}
 the sheaf $f'_*\mathcal{O}_{X'}$ is quasi-coherent on $Y$. Hence we win.
 \end{proof}