handle ansi styled prefix

followup to 0968122686180d01e1c9aca26527d7a465b28e05

before it didn't detect the end of the string correctly when it ended in an ansi escape.

also make sure the inserted `:` is inserted inside any ansi escape code.

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Noticed it when `yo` still showed `? 'Allo Sindre! What would you like to do?:` with the latest version of Inquirer.