with aliases, multiple values for the same flag don't work

[derhuerst]

I'm using mri@1.2.0.

const headerAliased = {alias: {H: 'header'}}

mri(['-H', 'one', '--header=two'])
// as expected: { _: [], H: 'one', header: 'two' }
mri(['-H', 'one', '--header', 'two'])
// as expected: { _: [], H: 'one', header: 'two' }
mri(['-H', 'one', '-H', 'two'], headerAliased)
// as expected: { _: [], H: [ 'one', 'two' ], header: [ 'one', 'two' ] }
mri(['--header', 'one', '--header', 'two'], headerAliased)
// as expected: { _: [], header: [ 'one', 'two' ], H: [ 'one', 'two' ] }

mri(['-H', 'one', '--header=two'], headerAliased)
// not expected: { _: [], H: 'one', header: 'one' }
mri(['-H', 'one', '--header', 'two'], headerAliased)
// not expected: { _: [], H: 'one', header: 'one' }