Upgrade to Httpcore 4.4.6

Closes gh-8082

Author: wilkinsona

spring-boot-dependencies/pom.xml

@@ -91,7 +91,7 @@
 		<htmlunit.version>2.21</htmlunit.version>
 		<httpasyncclient.version>4.1.2</httpasyncclient.version>
 		<httpclient.version>4.5.2</httpclient.version>
-		<httpcore.version>4.4.5</httpcore.version>
+		<httpcore.version>4.4.6</httpcore.version>
 		<infinispan.version>8.2.5.Final</infinispan.version>
 		<jackson.version>2.8.6</jackson.version>
 		<janino.version>2.7.8</janino.version>