fix sleep method in builtin

Author: yndu13

lib/builtin.js

@@ -394,8 +394,10 @@ class Func {
   }
 
   sleep(args) {
-    this.generator.emit('usleep');
-    this.generator.visitArgs(args);
+    this.generator.emit('usleep(');
+    const expr = args[0];
+    this.generator.visitExpr(expr);
+    this.generator.emit(' * 1000)');
   }
 
   equal(args){

tests/expected/builtin/Client.php

@@ -420,7 +420,7 @@ static public function main($args)
 
     }
 
-    usleep($a);
+    usleep($a * 1000);
     $defaultVal = ''.(@$args[0] ? @$args[0] : @$args[1]);
     if ($defaultVal === $b) {
       return null;