Fix partial minibatch computation in GAIL dataset.

[richardwu]

Description

Division was used incorrectly instead of modulus for checking if a partial minibatch exists.

Motivation and Context

Same as description.

• I have raised an issue to propose this change (required for new features and bug fixes)

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation (update in the documentation)

Checklist:

• I've read the CONTRIBUTION guide (required)
• I have updated the changelog accordingly (required).
• My change requires a change to the documentation.
• I have updated the tests accordingly (required for a bug fix or a new feature).
• I have updated the documentation accordingly.
• I have ensured pytest and pytype both pass (by running make pytest and make type).

[araffin]

Hello,
thanks for the PR. Please don't delete item from the PR check-list next time ;)
(and don't forget to add your username at the bottom of the changelog)

[richardwu]

Apologies for deleting the checkbox: I've added it back in :)

[araffin]

LGTM, thanks =)