Rename minimal formatter to failure list formatter
Created by: benoittgt
Address Myron comment on formatter name https://github.com/rspec/rspec-core/pull/2614/files#r283952925
"Minimal" is a subjective term -- I can imagine many different minimal formatters that output different things. Here it seems like this formatter is focused on printing a list of failures. WDYT about calling this FailureListFormatter? Seems like a more accurate name.