Update Simplecov formatter syntax
Update Simplecov formatter syntax

In https://github.com/colszowka/simplecov/pull/317 Simplecov changed how they
specify multiple formatters.  This change updates to the newer syntax.

tristaneuan/lita,litaio/lita,brodock/lita,tristaneuan/lita,jimmycuadra/lita,brodock/lita,litaio/lita,jimmycuadra/lita