fix(scripts): `dev` script cannot run successfully on Windows.

[plainheart]

When I run the command npm run dev on Windows, the terminal will throw some errors.

> npx concurrently --kill-others "npm run watch" "node build/server.js"

[1] 'run' �����ڲ����ⲿ���Ҳ���ǿ����еij���
[1] ���������ļ���
[2] 'watch' �����ڲ����ⲿ���Ҳ���ǿ����еij���
[2] ���������ļ���
[4] 'build' �����ڲ����ⲿ���Ҳ���ǿ����еij���
[4] ���������ļ���
[2] watch exited with code 1
--> Sending SIGTERM to other processes..
[1] run exited with code 1
--> Sending SIGTERM to other processes..
[4] build/server.js exited with code 1
--> Sending SIGTERM to other processes..
[0]
[0] Usage: npm <command>
[0]
[0] where <command> is one of:
[0]     access, adduser, audit, bin, bugs, c, cache, ci, cit,
[0]     clean-install, clean-install-test, completion, config,
[0]     create, ddp, dedupe, deprecate, dist-tag, docs, doctor,
[0]     edit, explore, fund, get, help, help-search, hook, i, init,
[0]     install, install-ci-test, install-test, it, link, list, ln,
[0]     login, logout, ls, org, outdated, owner, pack, ping, prefix,
[0]     profile, prune, publish, rb, rebuild, repo, restart, root,
[0]     run, run-script, s, se, search, set, shrinkwrap, star,
[0]     stars, start, stop, t, team, test, token, tst, un,
[0]     uninstall, unpublish, unstar, up, update, v, version, view,
[0]     whoami
[0]
[0] npm <command> -h  quick help on <command>
[0] npm -l            display full usage info
[0] npm help <term>   search for help on <term>
[0] npm help npm      involved overview

This may be a compatibility issue of concurrently, thus I made two changes to the dev script as follows:

(1) Replace the spaces in the command string with ':'

npm run watch -> npm:watch (shortened)

(2) Move node build/server.js to a new separate script server

"server": "node build/server.js"

As the above changes, the final script for dev will be:

npx concurrently --kill-others \"npm:watch\" \"npm:server\"

I've made some tests in Mac OS and Windows, the results are OK.

[pissang]

Thanks!