Upgrade maven-javadoc-plugin to 3.1.0

Change-Id: I4fc59b02e92db55797b9773648fd1dea88682ade
Signed-off-by: David Pursehouse <david.pursehouse@gmail.com>

pom.xml

@@ -199,7 +199,7 @@
     <httpcore-version>4.4.10</httpcore-version>
     <slf4j-version>1.7.2</slf4j-version>
     <log4j-version>1.2.15</log4j-version>
-    <maven-javadoc-plugin-version>3.0.1</maven-javadoc-plugin-version>
+    <maven-javadoc-plugin-version>3.1.0</maven-javadoc-plugin-version>
     <tycho-extras-version>1.3.0</tycho-extras-version>
     <gson-version>2.8.2</gson-version>
     <bouncycastle-version>1.60</bouncycastle-version>