Add apache http client to zuul deps. (#2889)

spring-cloud-netflix-zuul/pom.xml

@@ -17,6 +17,7 @@
     <description>Spring Cloud Netflix Zuul</description>
     <properties>
         <main.basedir>${basedir}/..</main.basedir>
+        <apachehttpclient.version>4.5.4</apachehttpclient.version>
     </properties>
 
     <dependencies>
@@ -25,6 +26,11 @@
             <artifactId>spring-cloud-netflix-core</artifactId>
         </dependency>
         <dependency>
+            <groupId>org.apache.httpcomponents</groupId>
+            <artifactId>httpclient</artifactId>
+            <version>${apachehttpclient.version}</version>
+        </dependency>
+        <dependency>
             <groupId>org.springframework.boot</groupId>
             <artifactId>spring-boot-configuration-processor</artifactId>
             <optional>true</optional>