Update gtfparse version requirement

[jpintar]

In 00ece88, gtfparse version was pinned to <2 because of confilcts between gtfparse and recent versions of polars. Since 12/21/23, with gtfparse v. 2.1.0, the conflicts have been eliminated, so there is no need to keep older versions pinned.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (12c103f) 56.20% compared to head (0b8d08d) 56.20%.

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #118 +/- ## ======================================= Coverage 56.20% 56.20% ======================================= Files 13 13 Lines 427 427 ======================================= Hits 240 240 Misses 187 187 ```

[grst]

Thanks for the heads-up!