volume3D incorrectly decamelizes volume_3d

[fc]

How to reproduce the issue:

const camelcase = require('camelcase');
const decamelize = require('decamelize');

console.log(camelcase('volume_3d')); // Output: volume3D
console.log(decamelize('volume3D'));  // Output: volume3_d

[sindresorhus]

console.log(decamelize('volume3D')); // Output: volume3_d

What is the expected output?

[dohomi]

@sindresorhus the expected output would be volume_3d.