Preserve formatting of package.json

See discussion in #38, which was originally meant to address #37 but ended up in a slippery slope of scope creep.

Basically, we overwrite package.json using JSON.stringify(pkg, null, 2) + '\n' but this may be too intrusive for folks using Windows line endings (\r\n instead of \n) or different indentation (tabs instead of spaces, or more than 2 spaces).

Here are a couple ways we could address this:

1. Detect and preserve newline chars and indentation via detect-newline and detect-indent (similar to #38)
2. Read package.json as string (instead of require()ing it) and just replace the "version" value, ignoring/preserving all other content/formatting

I think I’d prefer option 2.

I also think our CHANGELOG writing logic should not be affected by this.

[hugomrdias]

please preserve the code format, we are always fixing conflicts on package.json

[nexdrew]

Looks like npm version pretty much does the same thing that standard-version does. Hmm, maybe this is a non-issue then…