Upgrade to Guava 30.1.1

This addresses a security issue from by Dependabot that is not
relevant to modernizer.  Release notes:

https://github.com/google/guava/releases

Author: gaul

modernizer-maven-plugin/pom.xml

@@ -28,7 +28,7 @@
     <dependency>
       <groupId>com.google.guava</groupId>
       <artifactId>guava</artifactId>
-      <version>29.0-jre</version>
+      <version>30.1.1-jre</version>
       <scope>test</scope>
     </dependency>
     <dependency>