flow-remove-types produces invalid JS after non-latin characters

Flow version: 0.100.0

## Expected behavior

Given the following input:

```js
// @flow
// п
function foo(bar: number) {}
```

`flow-remove-types` should produce:

```js
//
// п
function foo(bar ) {}
```

## Actual behavior

It produces invalid JS:

```js
//
// п
function foo(bar: {}
```

The non-latin character is the trigger. Without it, it works correctly. This seems like quite a serious bug considering how common it is to use non-latin characters in comments (e.g. comment in other languages, draw arrows etc.).

cc @mroch @samwgoldman