--quiet mode reports todos as errors

[steveszc]

As noted in #394, eslint-formatter-todo is not properly processing results when run with eslint's --quiet flag.
This results in TODOs being displayed in the printed output, and the error counts incorrectly include todos.

The primary cause of this is noted here: #394 (comment)
(the filtered results used in quiet mode include todos, when it should only include errors)

eslint-formatter-todo/src/formatter.ts

Line 278 in 79792ef

return message.severity !== Severity.warn;