update httpclient to 4.5.8

Author: BCaxelbecker

pom.xml

@@ -27,7 +27,7 @@
 		<arangodb.velocypack.version>1.4.1</arangodb.velocypack.version>
 
 		<!-- provided -->
-		<httpclient.version>4.5.7</httpclient.version>
+		<httpclient.version>4.5.8</httpclient.version>
 
 		<!-- test -->
 		<logback-classic.version>1.1.3</logback-classic.version>