Update error handling.

commands/author.js

commands/avatar.js

commands/ban.js

commands/clear.js

commands/embed.js

commands/eval.js

commands/guild-info.js

commands/hug.js

commands/icon.js

commands/invite.js

commands/issue.js

commands/kick.js

commands/kiss.js

commands/leave-channel.js

commands/leave-message.js

commands/ping.js

commands/shutdown.js

commands/spoiler.js

commands/start-vote.js

commands/stats.js