Synchronize with node-emoji source

[petehouston]

The node-emoji json source has archived into legacy branch. Considering with we need to change the source constant

from

static final String EMOJI_SOURCE =
      'https://raw.githubusercontent.com/omnidan/node-emoji/master/lib/emoji.json';

to

static final String EMOJI_SOURCE =
      'https://raw.githubusercontent.com/omnidan/node-emoji/legacy/lib/emoji.json';