This still allocates a ton (a string for each line, plus a bunch of
splits into arrays), but it helps a bit when Bundler has to go through
dependency resolution.

```
==> memprof.after.txt <==
Total allocated: 194.14 MB (2317172 objects)
Total retained:  60.81 MB (593164 objects)

==> memprof.before.txt <==
Total allocated: 211.97 MB (2404890 objects)
Total retained:  62.85 MB (640342 objects)
```

https://github.com/rubygems/rubygems/commit/c68b41b0e5