timezone plugin broken in IE11 (unsupported method)

**Describe the bug**
`Intl.DateTimeFormat.formatToParts` is [not supported](https://caniuse.com/mdn-javascript_builtins_intl_datetimeformat_formattoparts) in IE11. This method is used by the timezone plugin [here](https://github.com/iamkun/dayjs/blob/9c20e77caf7b1b5eccf418175203b198d4e29535/src/plugin/timezone/index.js#L42). Using the plugin in IE11 results in a runtime error.

**Expected behavior**
IE11 support. Documentation states "Currently the following browsers are used for the ci system: Chrome on Windows XP, IE 8, 9, and 10 on Windows 7, IE 11 on Windows 10, latest Firefox on Linux, and latest Safari on OSX 10.8 and 10.11."

**Information**
- Day.js Version 1..10.4
- OS: Windows 10
- Browser IE11
- Time zone: GMT-07:00 DST (Pacific Daylight Time)

Start at src/plugin/timezone/index.js around line 42, where Intl.DateTimeFormat.formatToParts is used, and review the timezone plugin's browser-support setup. Reproduce the IE11 runtime error, then verify that the plugin works in IE11 without changing its expected timezone results.

Written by the indexing model from the issue text.