function resolveFromNpm (nodeModules, parentTarget, parsedSpec) {
	const {raw, name, type, spec} = parsedSpec
	log(`resolving ${raw} from npm`)
	const options = {...config.httpOptions, retries: config.retries}
	return registry.match(name, spec, options)::map((pkgJson) => {
		const target = pkgJson.dist.shasum
		log(`resolved ${raw} to tarball shasum ${target} from npm`)
		return {parentTarget, pkgJson, target, name, type, fetch}
	})
}
resolve a dependency's `package.json` file from the npm registry.
@param	{String} nodeModules - `node_modules` base directory.
@param	{String} parentTarget - relative parent's node_modules path.
@param	{Object} parsedSpec - parsed package name and specifier.
@return {Observable} - observable sequence of `package.json` objects.