use github ci instead of travis

[isidroas]

Thank you for this great project. For me, this is the best way to learn math.

I propose to drop travis, since it seems that it no longer supports open source projects.

The ci fails due to:

• pylint

  primes.py:47:4: W0237: Parameter 'value' has been renamed to 'prime' in overriding 'Primes.index' method (arguments-renamed)
  primes.py:276:0: C0103: Function name "_D_chooser" doesn't conform to snake_case naming style (invalid-name)
  
  -----------------------------------
  Your code has been rated at 9.94/10
  
  lint: exit 20 (1.93 seconds) /home/runner/work/primes.py/primes.py> pylint primes.py binary_search.py pid=2033
  

• mypy

  typing: commands[0]> mypy primes.py binary_search.py --strict
  binary_search.py:18: error: No overload variant of "bisect_left" matches argument types "Sequence[T]", "T", "int", "int"  [call-overload]
  binary_search.py:18: note: Possible overload variants:
  binary_search.py:18: note:     def [SupportsRichComparisonT] bisect_left(a: SupportsLenAndGetItem[SupportsRichComparisonT], x: SupportsRichComparisonT, lo: int = ..., hi: int | None = ..., *, key: None = ...) -> int
  binary_search.py:18: note:     def [_T, SupportsRichComparisonT] bisect_left(a: SupportsLenAndGetItem[_T], x: SupportsRichComparisonT, lo: int = ..., hi: int | None = ..., *, key: Callable[[_T], SupportsRichComparisonT]) -> int
  binary_search.py:19: error: Returning Any from function declared to return "int"  [no-any-return]
  binary_search.py:26: error: Value of type variable "SupportsRichComparisonT" of "bisect_right" cannot be "object"  [type-var]
  Found 3 errors in 1 file (checked 2 source files)
  typing: exit 1 (2.79 seconds) /home/runner/work/primes.py/primes.py> mypy primes.py binary_search.py --strict pid=2089
  py311: OK (33.70=setup[8.89]+cmd[24.82] seconds)
  lint: FAIL code 20 (9.37=setup[7.43]+cmd[1.93] seconds)
  typing: FAIL code 1 (10.67=setup[7.88]+cmd[2.79] seconds)
  evaluation failed :( (53.81 seconds)