Fix npmjs domain in README

[simeji]

Changed npm domain to npmjs.com from npmjs.org.

Failure

ubuntu@ubuntu17:~$ curl -0 -L https://npmjs.org/install.sh | sudo sh
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0curl: (6) Could not resolve host: npmjs.org

curl npmjs.org

ubuntu@ubuntu17:~$ curl npmjs.org -I
HTTP/1.1 301 Moved Permanently
Server: nginx/1.4.6 (Ubuntu)
Date: Sat, 11 Feb 2017 10:27:36 GMT
Content-Type: text/html
Content-Length: 193
Connection: keep-alive
Location: https://www.npmjs.com/

After npmjs.org => npmjs.com, I get Succeed.

curl -0 -L https://npmjs.com/install.sh | sudo sh
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  0   193    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0
100  6263  100  6263    0     0   2932      0  0:00:02  0:00:02 --:--:--  764k
tar=/bin/tar
version:
...
...
...

[sam3d]

LGTM 👍

[troy0820]

LGTM 👍