ES6 Static code import `protobufjs` isntead of `protobufjs/minimal`

protobuf.js version: 6.7.3

**Actual behavior**

When generating static code with `es6` wrapping like so:
```shell
$pbjs -w es6 -t static-module message.proto > message.js
```

The `message.js` script imports `protobufjs`:
```js
import * as $protobuf from "protobufjs";
```

**Expected behavior**
The `message.js` script should import `protobufjs/minimal`, isn't it?
