refactor: export as ES2015 Module (#10)

feat: Export as ES Module

BREAKING CHANGE: ES Modules are not compatible with Webpack v1.x

index.js

@@ -5,5 +5,5 @@
 module.exports = function(content) {
 	this.cacheable && this.cacheable();
 	this.value = content;
-	return "module.exports = " + JSON.stringify(content);
+	return "export default " + JSON.stringify(content);
 }