Handle first time display of dependencies

[tommy-mitchell]

Fixes #699. util.getNewDependencies currently fails on first publish, as there's no previous release to read a package.json from:

np/source/util.js

Lines 86 to 90 in 0651933

	export const getNewDependencies = async (newPkg, rootDir) => {
	let oldPkg = await git.readFileFromLastRelease(path.resolve(rootDir, 'package.json'));
	oldPkg = JSON.parse(oldPkg);
	const newDependencies = [];

#689 should add a test case for this.