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/nullable/__snapshots__/jsfmt.spec.js.snap

@@ -42,9 +42,11 @@ function bar(): ?string {
   return null;
 }
 
-function qux(x: string) {}
+function qux(x: string) {
+}
 
-function corge(x: number) {}
+function corge(x: number) {
+}
 
 var x = bar();
 // x: ?string
@@ -73,12 +75,15 @@ bar(\'hmm\');
 function fn(data: ?{}) {}
 fn({some: \'literal\'});
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-function foo(x: ?string) {}
-function bar(x: ?number) {}
+function foo(x: ?string) {
+}
+function bar(x: ?number) {
+}
 foo(\"hmm\");
 bar(\"hmm\");
 
-function fn(data: ?{}) {}
+function fn(data: ?{}) {
+}
 fn({ some: \"literal\" });
 "
 `;