push newline after decorator when doing code gen - fixes #1713

src/babel/generation/generators/expressions.js

@@ -70,6 +70,7 @@ export function Super() {
 export function Decorator(node, print) {
   this.push("@");
   print.plain(node.expression);
+  this.newline();
 }
 
 export function CallExpression(node, print) {