Skygear 1.7.1 does not work in Safari of iOS 10

[yipsang]

(Describe the issue here)

• Skygear SDK Date/Version: 1.7.1
• JS runtime: Safari iOS 10
• Skygear Server Date/Version: 1.7.1
• Is this a regression?
• Attached logs, screenshots
  

Expected Results

Able to import skygear via <script src="https://code.skygear.io/js/skygear/1.7.1/skygear.min.js"></script>

Actual Results

Unable to import skygaer

[rickmak]

Let consider to use terser-js?