bugfix: convert windows \r\n to unix-style \n

[coolaj86]

As per #156 (comment)

[joho]

I don't believe conversion is the appropriate solution.

1. People who put specific linebreaks in an env var may very well have a good reason for it
2. Ruby dotenv preserves them, and in general I try and preserve compatiblity/portability of env files between implementations

[coolaj86]

Oh, I thought the test was failing on Windows because it preserved them. I must have misinterpreted the logs.