Upgrade com.google.guava:guava to 30.0-jre in the maven example.

Closes https://github.com/google/dagger/pull/3603

RELNOTES=n/a
PiperOrigin-RevId: 484635512
diff --git a/examples/maven/pom.xml b/examples/maven/pom.xml
index be21b96..69c7221 100644
--- a/examples/maven/pom.xml
+++ b/examples/maven/pom.xml
@@ -49,7 +49,7 @@
       <dependency>
         <groupId>com.google.guava</groupId>
         <artifactId>guava</artifactId>
-        <version>26.0-jre</version>
+        <version>30.0-jre</version>
       </dependency>
     </dependencies>
   </dependencyManagement>