Upgrade maven-javadoc-plugin to 3.1.1

Change-Id: I199dc24e6ad608b6420d00005acc51cfd771e852

pom.xml

diff --git a/pom.xml b/pom.xml
index de72eea..385221f 100644
--- a/pom.xml
+++ b/pom.xml
@@ -419,7 +419,7 @@
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-javadoc-plugin</artifactId>
-        <version>3.0.1</version>
+        <version>3.1.1</version>
         <configuration>
           <encoding>UTF-8</encoding>
           <quiet>true</quiet>