lib: changed var to const in internal/v8_polyfill

PR-URL: #8615
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

lib/internal/v8_prof_polyfill.js

@@ -67,13 +67,13 @@ var line = '';
 versionCheck();
 function readline() {
   while (true) {
-    var lineBreak = line.indexOf('\n');
+    const lineBreak = line.indexOf('\n');
     if (lineBreak !== -1) {
-      var res = line.slice(0, lineBreak);
+      const res = line.slice(0, lineBreak);
       line = line.slice(lineBreak + 1);
       return res;
     }
-    var bytes = fs.readSync(fd, buf, 0, buf.length);
+    const bytes = fs.readSync(fd, buf, 0, buf.length);
     line += dec.write(buf.slice(0, bytes));
     if (line.length === 0) {
       return false;