Upgrade spotbugs to 3.1.6

Change-Id: Id84497107ef9ee2eca3c9d65197ab8c14f492655
Signed-off-by: David Pursehouse <david.pursehouse@gmail.com>

pom.xml

@@ -216,7 +216,7 @@
     <maven-javadoc-plugin-version>3.0.1</maven-javadoc-plugin-version>
     <tycho-extras-version>1.2.0</tycho-extras-version>
     <gson-version>2.8.2</gson-version>
-    <spotbugs-maven-plugin-version>3.1.5</spotbugs-maven-plugin-version>
+    <spotbugs-maven-plugin-version>3.1.6</spotbugs-maven-plugin-version>
     <maven-surefire-report-plugin-version>2.21.0</maven-surefire-report-plugin-version>
 
     <!-- Properties to enable jacoco code coverage analysis -->