Upgrade to Httpcore 4.4.8

Closes gh-10630

Author: wilkinsona

spring-boot-dependencies/pom.xml

@@ -94,7 +94,7 @@
 		<htmlunit.version>2.21</htmlunit.version>
 		<httpasyncclient.version>4.1.3</httpasyncclient.version>
 		<httpclient.version>4.5.3</httpclient.version>
-		<httpcore.version>4.4.7</httpcore.version>
+		<httpcore.version>4.4.8</httpcore.version>
 		<infinispan.version>8.2.8.Final</infinispan.version>
 		<jackson.version>2.8.10</jackson.version>
 		<janino.version>2.7.8</janino.version>