Syntax Highlighting errors in flow with generics

![flow](https://user-images.githubusercontent.com/13142418/51796730-954be900-2232-11e9-8336-90e4c86ff061.png)

Highlight this code correctly:

```
type Test2<A> = A;
type Test = Test2<{}>;
type Test3 = string;
```

ref: https://github.com/SpaceVim/SpaceVim/issues/2458