refactor(problems): update http-client problem definition

problems/http_client/problem.txt

@@ -11,7 +11,7 @@ To make a POST request, just call `request.post()` instead of `request()`:
 
     var request = require('request');
     var r = request.post('http://beep.boop:80/');
-    
+
 The `r` object that you get back from `request.post()` is a readable+writable
 stream so you can pipe a readable stream into it (`src.pipe(r)`) and you can
 pipe it to a writable stream (`r.pipe(dst)`).
@@ -20,5 +20,7 @@ You can even chain both steps together: src.pipe(r).pipe(dst);
 
 Hint: for your code, src will be process.stdin and dst will be process.stdout.
 
-Make sure to `npm install request` in the directory where your solution file
-lives.
+Make sure to do the following before verifying your solution:
+- `npm install request` in the directory where your solution file lives.
+- free port 8099 for the testing server by temporarily closing
+other applications that use it, i.e. installing a module like node-portfinder.