[Fix #1111] Fix reading of non-UTF-8 files in EndOfLine

The problem was that we used `buffer.source.encoding` as the file's encoding when reading it again, but [Parser](https://github.com/whitequark/parser) has re-encoded the buffer so it's always UTF-8. By first reading the file as `ascii-8bit` ("binary") encoding, and then re-encoding it based on Parser's logic for recognizing encodings, we should be able to match `/\r$/` always.