Fix datepicker modal-content display

[gaw89]

Proposed changes

Screenshots (if appropriate) or codepen:

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).

Checklist:

• I have read the CONTRIBUTING document.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

This fixes a very minor issue in the display of the datepicker component. Currently, the component looks like this:

As you can see, there is a 4px margin at the bottom which causes a blank space in the background of the date display. With this update, the datepicker modal looks like this:

This is how it looked in the previous version of Materialize.

Thanks for a great library!