Support node.js

[hackerwins]

Description:

General JS SDK supports not only Browser but also NodeJS(For example, Firebase JS SDK works well with NodeJS: Link).

However, the Yorkie JS SDK has yet to implement support for browsers only. Let's make it work well in NodeJS as well.

Why:

• Users using NodeJS can also use Yorkie.

[CharlesSampson44]

import xhr2 from "xhr2"; global.XMLHttpRequest = xhr2;

and it works...

[blurfx]

I've done some research and it looks like xhr2 could be a way to use yorkie-js-sdk in node.js, but it's not a clean way because the yorkie-js-sdk needs to verify that you are in a node environment and set the xhr2 shim.

Also grpc-webusesXMLHttpRequest, so I don't think we'll be able to support it anytime soon.

So, I think using connect-web(#375) instead of grpc-web is better way.

[hackerwins]

Related to https://github.com/yorkie-team/yorkie/issues/668