Trac #25333: Feature check for plantri is broken

It should test for "1 triangulations written" instead of "1
triangulation written"

URL: https://trac.sagemath.org/25333
Reported by: jdemeyer
Ticket author(s): Frédéric Chapoton
Reviewer(s): Vincent Delecroix

src/sage/features/graph_generators.py

@@ -47,7 +47,7 @@ def is_functional(self):
             return FeatureTestResult(self, False,
                     reason="Call `{command}` failed with exit code {e.returncode}".format(command=" ".join(command), e=e))
 
-        expected = "1 triangulation written"
+        expected = "1 triangulations written"
         if lines.find(expected) == -1:
             return FeatureTestResult(self, False,
                     reason = "Call `{command}` did not produce output which contains `{expected}`".format(command=" ".join(command), expected=expected))