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.

src/printer.js

@@ -492,11 +492,6 @@ function genericPrintNoParens(path, options, print) {
       const hasContent = getFirstString(naked);
       const hasDirectives = n.directives && n.directives.length > 0;
 
-      // If there are no contents, return a simple block
-      if (!hasContent && !hasDirectives) {
-        return "{}";
-      }
-
       parts.push("{");
 
       // Babel 6