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/arraylib/__snapshots__/jsfmt.spec.js.snap

@@ -58,7 +58,8 @@ function from_test() {
 }
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 /* @flow */
-function foo(x: string) {}
+function foo(x: string) {
+}
 
 var a = [ 0 ];
 var b = a.map(function(x) {