Absolute imports do not auto resolve to index.js files in node resolution mode

Affects:

```
Version: v20200927.0.0
Built on: 2020-09-29 11:30
```

Inputs:

```javascript
// main.js
import { A } from 'foo';
console.log(A);

// foo/index.js
export const A = 'B';
```

Command:

```
java -jar compiler.jar -O ADVANCED --language_out ECMASCRIPT_2017 --module_resolution NODE --js main.js --js foo/index.js
```

Errors:

```
main.js:1:0: ERROR - [JSC_JS_MODULE_LOAD_WARNING] Failed to load module "foo"
1| import { A } from 'foo';
^
```

Expected output: No error

Notes: Relative imports (`import { A } from './foo'`) works as expected, outputs:

```javascript
'use strict';console.log("B");
```