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/classes/__snapshots__/jsfmt.spec.js.snap

@@ -6,7 +6,8 @@ exports[`test A.js 1`] = `
 module.exports = A;
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 class A {
-  foo(x: number): void {}
+  foo(x: number): void {
+  }
 }
 
 module.exports = A;
@@ -49,7 +50,8 @@ module.exports = C;
 var B = require(\"./B\");
 
 class C extends B {
-  foo(x: string): void {}
+  foo(x: string): void {
+  }
 }
 
 let c = new C();