Update fixtures/emojis/aliases.json

Also adds a script to re-generate them from the index.

fixtures/emojis/generate_aliases.rb

+#!/usr/bin/env ruby
+
+require 'json'
+
+aliases = {}
+
+index_file = File.expand_path("./index.json")
+index = JSON.parse(File.read(index_file))
+
+index.each_pair do |key, data|
+  data['aliases'].each do |a|
+    a.tr!(':', '')
+
+    aliases[a] = key
+  end
+end
+
+puts JSON.pretty_generate(aliases, indent: '   ', space: '', space_before: '')