chore(package): Version 3.1.1

2.0.1

- Fixed test cases

2.0.0

- `FlightDesignator.parse()` doesn't throw anymore when given
  an invalid input, instead returns `null`
- Added two more test cases and fixed `.parse()` according to them

1.0.1

- Fixed flight numbers with whitespace not being parsed
- Fixed single letter airline codes not throwing
- Fixed flight numbers with > 3 leading zeroes not throwing