Add newline for empty blocks {} (#205)

I find it weird to put `{}` together. So I figured I would change it to have an empty line and ask for feedback :)

![image](https://cloud.githubusercontent.com/assets/197597/21739279/062adc80-d44c-11e6-8bb7-5e0768f3ddde.png)

Beware: most of the test cases are not representative of real code, you almost never define blocks with no content in practice.

tests/undefined/__snapshots__/jsfmt.spec.js.snap

@@ -22,7 +22,8 @@ function doSomethingAsync(): Promise<void> {
 }
 
 // simpler repro to show that too few args are fine when expecting void
-function foo(x: void) {}
+function foo(x: void) {
+}
 foo();
 "
 `;
@@ -50,7 +51,8 @@ function bar() {
   if (x) x.bar();
 }
 
-function qux(x?: number, y: string = \"\", z) {}
+function qux(x?: number, y: string = \"\", z) {
+}
 "
 `;