edit How to use for httpclient 4.2-

Author: sekikatsu36

jvm/apache-httpclient/README.md

@@ -8,8 +8,8 @@ Add `M3TracingHttpInterceptor` as request/response interceptor of HttpClient.
 
 ```java:
 // CAUTION: Must setup as BOTH interceptor otherwise it may cause memory leak.
-httpclient.addRequestInterceptor(M3TracingHttpInterceptor.INSTANCE);
-httpclient.addResponseInterceptor(M3TracingHttpInterceptor.INSTANCE);
+httpclient.addRequestInterceptor(M3TracingHttpInterceptor.getINSTANCE());
+httpclient.addResponseInterceptor(M3TracingHttpInterceptor.getINSTANCE());
 ```
 
 ### httpclient 4.3+