Upgraded ktlint-maven-plugin from 0.9.19 to 0.9.21 (#137)

Bumps [ktlint-maven-plugin](https://github.com/gantsign/ktlint-maven-plugin) from 0.9.19 to 0.9.21.
- [Release notes](https://github.com/gantsign/ktlint-maven-plugin/releases)
- [Commits](gantsign/ktlint-maven-plugin@0.9.19...0.9.21)

Signed-off-by: dependabot[bot] <support@dependabot.com>

Author: dependabot[bot]

pom.xml

@@ -457,7 +457,7 @@
       <plugin>
         <groupId>com.github.gantsign.maven</groupId>
         <artifactId>ktlint-maven-plugin</artifactId>
-        <version>0.9.19</version>
+        <version>0.9.21</version>
         <executions>
           <execution>
             <id>format-and-check</id>