Add a missing word in solver documentation (#2376)
diff --git a/doc/solver.md b/doc/solver.md
index 9d8c8ba..30605db 100644
--- a/doc/solver.md
+++ b/doc/solver.md
@@ -205,7 +205,7 @@
A derivation graph represents a proof that the terms in its root incompatibility
are in fact incompatible. Because all derived incompatibilities track their
causes, we can find a derivation graph for any of them and thereby prove it. In
-particular, when Pubgrub determines that no solution can be found, uses the
+particular, when Pubgrub determines that no solution can be found, it uses the
derivation graph for the incompatibility `{root any}` to
[explain to the user](#error-reporting) why no versions of the root package can
be selected and thus why version solving failed.
