Fix RegexpError when parsing command

[kuboshizuma]

Regexp error happens when receiving meta character for commands.
This commit makes commands escaped.

[kuboshizuma]

Oops, should we change settings for RuboCop?

lib/slack-ruby-bot/commands/base.rb:3:5: C: Class has too many lines. [101/100]
    class Base
    ^^^^^
62 files inspected, 1 offense detected
RuboCop failed!

[dblock]

This is great, thanks! Update CHANGELOG please. For RuboCop run rubocop --auto-gen-config. Commit via --amend.

[kuboshizuma]

Thank you for changing settings for RuboCop!
Now, update commit following your comment.

[dblock]

Still needs an entry in CHANGELOG, please.

[kuboshizuma]

I commit again for CHANGELOG.
Is it all right?

[dblock]

Looks great, merging. Thanks.