Bump sign-maven-plugin from 0.3.0 to 0.3.1

Bumps [sign-maven-plugin](https://github.com/s4u/sign-maven-plugin) from 0.3.0 to 0.3.1.
- [Release notes](https://github.com/s4u/sign-maven-plugin/releases)
- [Commits](s4u/sign-maven-plugin@v0.3.0...v0.3.1)

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

pom.xml

@@ -130,7 +130,7 @@
         <maven-surefire-plugin.version>3.0.0-M5</maven-surefire-plugin.version>
         <nexus-staging-maven-plugin.version>1.6.8</nexus-staging-maven-plugin.version>
         <plexus-component-metadata.version>2.1.0</plexus-component-metadata.version>
-        <sign-maven-plugin.version>0.3.0</sign-maven-plugin.version>
+        <sign-maven-plugin.version>0.3.1</sign-maven-plugin.version>
         <sitemapxml-maven-plugin.version>2.1.0</sitemapxml-maven-plugin.version>
         <versions-maven-plugin.version>2.8.1</versions-maven-plugin.version>
     </properties>