Update Spring Security to 4.2.20.RELEASE

Closes gh-1919

Author: jgrandja

pom.xml

@@ -20,7 +20,7 @@
     <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
     <commons-codec.version>1.14</commons-codec.version>
     <spring.version>4.3.30.RELEASE</spring.version>
-    <spring.security.version>4.2.15.RELEASE</spring.security.version>
+    <spring.security.version>4.2.20.RELEASE</spring.security.version>
     <spring.data.redis.version>1.5.2.RELEASE</spring.data.redis.version>
     <redis.clients.version>2.6.3</redis.clients.version>
     <junit.version>4.12</junit.version>