Bump Sparkjava version to address volnerabilities in older dependencies

Author: sapessi

aws-serverless-java-container-spark/pom.xml

@@ -16,7 +16,7 @@
     </parent>
 
     <properties>
-        <spark.version>2.8.0</spark.version>
+        <spark.version>2.9.1</spark.version>
     </properties>
 
     <dependencies>