Upgrade to Httpclient 4.5.3

Closes gh-8359

Author: wilkinsona

spring-boot-dependencies/pom.xml

@@ -90,7 +90,7 @@
 		<hsqldb.version>2.3.3</hsqldb.version>
 		<htmlunit.version>2.21</htmlunit.version>
 		<httpasyncclient.version>4.1.3</httpasyncclient.version>
-		<httpclient.version>4.5.2</httpclient.version>
+		<httpclient.version>4.5.3</httpclient.version>
 		<httpcore.version>4.4.6</httpcore.version>
 		<infinispan.version>8.2.5.Final</infinispan.version>
 		<jackson.version>2.8.7</jackson.version>