Reject edited messages

[00-1]

Check for and reject messages with edited parameter.

e.g.

{ event_time: 1534252977,
  event: 
   { client_msg_id: 'b2968c58-a0f7-42c9-81ca-aa0b8987b713',
     event_ts: '1534252977.000100',
     user: 'U81J2C10D',
     text: '<@UC6T0FNDV> it\'s slightly faster in theory but still doesn\'t buy any bitcoin',
     type: 'app_mention',
     ts: '1534252977.000100',
---> edited: { ts: '1534253000.000000', user: 'U81J2C10D' },
     channel: 'G9UHKMCAK' },
  team_id: 'T80Q0U7DW',
  type: 'event_callback',
  api_app_id: 'AC527HL1W',
  token: 'W2xUCtWmvz8ceA9ldDRStleu',
  authed_users: [ 'UC6T0FNDV' ],
  event_id: 'EvC99T5KGF' 
}