Bump checkstyle from 9.0.1 to 9.1 apache#194.

Author: garydgregory

src/changes/changes.xml

@@ -41,7 +41,7 @@
     <release version="1.9.1" date="2021-MM-DD" description="Feature and bug fix release (Java 8)">
       <action                 type="update" dev="ggregory" due-to="Arturo Bernal">Minor changes #172.</action>
       <!-- UPDATE -->
-      <action                 type="update" dev="ggregory" due-to="Dependabot">Bump checkstyle from 8.44 to 9.0.1 #180, #190.</action>
+      <action                 type="update" dev="ggregory" due-to="Dependabot">Bump checkstyle from 8.44 to 9.1 #180, #190, #194.</action>
       <action                 type="update" dev="ggregory" due-to="Dependabot">Bump junit-jupiter from 5.8.0-M1 to 5.8.1 #179, #186.</action>
       <action                 type="update" dev="ggregory" due-to="Dependabot">Bump jmh-core from 1.32 to 1.33 #176.</action>
       <action                 type="update" dev="ggregory" due-to="Dependabot">Bump jmh-generator-annprocess from 1.32 to 1.33 #175.</action>