Fix readJSON docs

[zcei]

Currently the docs do not match the actual behavior of the library.

readJSON never actually attempts to read a non-existent file, but guards it with an exists call:

mem-fs-editor/lib/actions/read-json.js

Lines 4 to 12 in 2c0ad36

	if (this.exists(filepath)) {
	try {
	return JSON.parse(this.read(filepath));
	} catch (error) {
	throw new Error('Could not parse JSON in file: ' + filepath + '. Detail: ' + error.message);
	}
	} else {
	return defaults;
	}

[SBoudrias]

Thanks!!