Fix endDate argument of makeListOfScanDatesFile

[lmoureaux]

Description

A typo prevented it from working correctly.

Types of changes

• [x] 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)

Motivation and Context

Reported in issue #144.

How Has This Been Tested?

Ran plotTimeSeries.py with both --startDate and --endDate, then checked that the contents of listOfScanDates.txt were within the specified range.

Checklist:

• [x] My code follows the code style of this project.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [ ] I have added tests to cover my changes.
• [x] All new and existing tests passed.