Upgrade to org.apache.httpcomponents:httpasyncclient 4.1

Closes gh-3188

spring-boot-dependencies/pom.xml

@@ -79,7 +79,7 @@
 		<hikaricp.version>2.3.8</hikaricp.version>
 		<hornetq.version>2.4.7.Final</hornetq.version>
 		<hsqldb.version>2.3.2</hsqldb.version>
-		<httpasyncclient.version>4.0.2</httpasyncclient.version>
+		<httpasyncclient.version>4.1</httpasyncclient.version>
 		<httpclient.version>4.4.1</httpclient.version>
 		<infinispan.version>7.2.2.Final</infinispan.version>
 		<jackson.version>2.5.4</jackson.version>