Upgrade Spotbugs to 3.1.8

Change-Id: Ie283ab9d9925c4eae3fad2a3ad2d94bdcb80f75f
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>3.1.7</spotbugs-maven-plugin-version>
+    <spotbugs-maven-plugin-version>3.1.8</spotbugs-maven-plugin-version>
     <maven-surefire-version>2.22.1</maven-surefire-version>
     <maven-compiler-plugin-version>3.8.0</maven-compiler-plugin-version>
     <maven-project-info-reports-plugin-version>3.0.0</maven-project-info-reports-plugin-version>