Unable to select a single day when the intended day equals the start or the end of a previously selected date range

Environment

• Package version(s): 3.11.0
• Browser and OS versions: Google Chrome 76 on macOS 10.14.5

Sandbox: https://codesandbox.io/s/blueprint-sandbox-wsj6f

Steps to reproduce

1. Select a date range, e.g. from the 3rd of August to the 15th of August.
2. Now you want to select the 3rd of August as a single-day range.
3. When clicking on this day, you are unable to select it since it is already the start of the previously selected date range.
4. The same applies if you want to use the last day of the previously selected date range, the 15th of August.

Actual behavior

When clicking the days in 3. and 4. the buttons are deselected.

Expected behavior

When clicking the days in 3. and 4. the buttons keep selected and can be used for a new single-day range.