Dosbox-staging: [IMGMOUNT] typo

[nemo93]

Describe the bug
It's not a bug just a typo in IMGMOUNT output.

To Reproduce
In DOSBox just type in something similar to the following:

C:\>IMGMOUNT D MY.ISO -T TEST

Expected behaviour
To be consistent with that command help page I'd expect cdrom to be listed as supported format instead of iso.

Version of dosbox-staging:
Current master.

Additional context
https://github.com/dosbox-staging/dosbox-staging/pull/577

[kcgen]

Thanks @nemo93 , we'll add cdrom to the list!