http: simplify isInvalidPath

The loop unrolling shows no performance benefits in V8 6.3.
This change is to simplify `isInvalidPath` without performance
regression.

lib/_http_client.js

@@ -51,20 +51,7 @@ const errors = require('internal/errors');
 // This function is used in the case of small paths, where manual character code
 // checks can greatly outperform the equivalent regexp (tested in V8 5.4).
 function isInvalidPath(s) {
-  var i = 0;
-  if (s.charCodeAt(0) <= 32) return true;
-  if (++i >= s.length) return false;
-  if (s.charCodeAt(1) <= 32) return true;
-  if (++i >= s.length) return false;
-  if (s.charCodeAt(2) <= 32) return true;
-  if (++i >= s.length) return false;
-  if (s.charCodeAt(3) <= 32) return true;
-  if (++i >= s.length) return false;
-  if (s.charCodeAt(4) <= 32) return true;
-  if (++i >= s.length) return false;
-  if (s.charCodeAt(5) <= 32) return true;
-  ++i;
-  for (; i < s.length; ++i)
+  for (var i = 0; i < s.length; ++i)
     if (s.charCodeAt(i) <= 32) return true;
   return false;
 }