Use default SimpleCov.formatter
Use default SimpleCov.formatter

coverage/covered_percent is for Cane gem
and Cane is removed at #202.
`cc-test-reporter` uses `coverage/.resultset.json`.

### Keep stopping HTML output in CI?

It is ECO, but not the default behavior of SimpleCov.
HTMLFormatter is SimpleCov's default formatter. (even in CI)

lostisland/faraday_middleware,lostisland/faraday_middleware