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/binary/__snapshots__/jsfmt.spec.js.snap

@@ -99,11 +99,14 @@ let tests = [
   },
   // in predicates
   function() {
-    if (\"foo\" in 123) {}
+    if (\"foo\" in 123) {
+    }
     // error
-    if (!\"foo\" in {}) {}
+    if (!\"foo\" in {}) {
+    }
     // error, !\'foo\' is a boolean
-    if (!(\"foo\" in {})) {}
+    if (!(\"foo\" in {})) {
+    }
   },
   // annotations on RHS
   function(x: Object, y: mixed) {