Empty return throws exception

```
function xd() {
  return
}
```

```
Compiler.js:60
                    throw exception;
                    ^
TypeError: Cannot read property 'kind' of undefined
    at LuaTranspiler.transpileExpression (Transpiler.js:309:21)
    at LuaTranspiler.transpileReturn (Transpiler.js:306:33)
    at LuaTranspiler.transpileNode (Transpiler.js:92:43)
```