upgrade jackson for jackson-databind is vulnerable to Deserialisation (#260)

Author: thomaszurkan-optimizely

gradle.properties

@@ -13,7 +13,7 @@ org.gradle.parallel = true
 gsonVersion = 2.6.1
 guavaVersion = 19.0
 hamcrestVersion = 1.3
-jacksonVersion = 2.9.6
+jacksonVersion = 2.9.8
 jsonVersion = 20160212
 jsonSimpleVersion = 1.1.1
 logbackVersion = 1.1.5