Upgrade maven-javadoc-plugin to 3.1.1

Change-Id: If1681581798d1f8b314b506680a75ec7becc1241
Signed-off-by: David Pursehouse <david.pursehouse@gmail.com>

pom.xml

diff --git a/pom.xml b/pom.xml
index 8c46d64..a07c3cc 100644
--- a/pom.xml
+++ b/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>3.1.0</maven-javadoc-plugin-version>
+    <maven-javadoc-plugin-version>3.1.1</maven-javadoc-plugin-version>
     <tycho-extras-version>1.3.0</tycho-extras-version>
     <gson-version>2.8.2</gson-version>
     <bouncycastle-version>1.61</bouncycastle-version>