fix: add Object.is ponyfill to improve ie compatibility

[NaccOll]

Summary

use ponyfill to replace Object.is due to ie compatibility.

Test plan

➜  loadable-components git:(add-Object.is-ponyfill) ✗ yarn test
yarn run v1.16.0
$ jest
 PASS  packages/server/src/util.test.js
 PASS  packages/server/src/ChunkExtractor.test.js
 PASS  packages/component/src/loadable.test.js
 PASS  packages/babel-plugin/src/index.test.js

Test Suites: 4 passed, 4 total
Tests:       83 passed, 83 total
Snapshots:   55 passed, 55 total
Time:        3.961s
Ran all test suites.
Done in 5.60s.

[theKashey]

cacheKey is expected to be just a string. Do we even need Object.is comparison?

[NaccOll]

@theKashey I don't know the previous design. I found that starting from 5.10.0, I can't open the page after using this dependency in IE browser. So I submit the pr.

[gregberge]

Fixed in #392