SourceMap URL not appended when Babili is executed from JS API

Hi guys, I'm trying to use babili from JS API but I'm having a problem. If I use it from CLI in this way:
```
babel ./build/popper.js --inputSourceMap=./build/popper.js.map -s -o ./build/popper.min.js
```
The resulting `popper.min.js` file will have at its bottom the comment:

```
//# sourceMappingURL=popper.min.js.map
```

If, instead, I use it from JS:

```
const options = {
presets: ['babili', 'stage-2'],
comments: false,
minified: true,
compact: true,
sourceMaps: true,
inputSourceMap: JSON.parse(fs.readFileSync(`${input}.map`, { encoding: 'utf8' })),
};
const result = babel.transform(inputCode, options);
```

The resulting code has not the source map comment. Do you know what I'm doing wrong?

For reference, this is the whole script:
```
// Not working...

const argv = require('yargs').argv;
const babel = require('babel-core');
const fs = require('fs');
const path = require('path');

const input = path.resolve(process.cwd(), argv.i);
const output = path.resolve(process.cwd(), argv.o);
const outputMap = `${output}.map`;

const inputCode = fs.readFileSync(input, { encoding: 'utf8' });
const inputSourceMap = JSON.parse(fs.readFileSync(`${input}.map`, { encoding: 'utf8' }));

// Generate options
//=================
const options = {
presets: [
'babili',
!!argv.es5 && ['es2015', { modules: false }],
'stage-2',
],
comments: false,
minified: true,
compact: true,
sourceMaps: true,
inputSourceMap,
};

options.presets = options.presets.filter(a => !!a);

// Transform code
//===============
const result = babel.transform(inputCode, options);

// Write output files
//===================
fs.writeFileSync(output, result.code);
fs.writeFileSync(outputMap, JSON.stringify(result.map));

```