PHP version bump from 7.1 to 7.3 and support for 7.4

[waahhhh]

Provide a narrative description of what you are trying to accomplish: I have checked https://www.php.net/supported-versions.php and noticed the support of the php versions 7.1 & 7.2 (in .travis.yml) ends.

• [ ] Are you fixing a bug?

  • [ ] Detail how the bug is invoked currently.
  • [ ] Detail the original, incorrect behavior.
  • [ ] Detail the new, expected behavior.
  • [ ] Base your feature on the master branch, and submit against that branch.
  • [ ] Add a regression test that demonstrates the bug, and proves the fix.
  • [ ] Add a CHANGELOG.md entry for the fix.

• [ ] Are you creating a new feature?

  • [ ] Why is the new feature needed? What purpose does it serve?
  • [ ] How will users use the new feature?
  • [ ] Base your feature on the develop branch, and submit against that branch.
  • [ ] Add only one feature per pull request; split multiple features over multiple pull requests
  • [ ] Add tests for the new feature.
  • [ ] Add documentation for the new feature.
  • [ ] Add a CHANGELOG.md entry for the new feature.

• [x] Is this related to quality assurance?

• Support for PHP 7.1 and PHP 7.2 ends

• Support for PHP 7.4 added

• [ ] Is this related to documentation?

[michalbundyra]

@waahhhh Thanks for your contribution.

Due to very close migration to Laminas and no any significant changes here I am closing it, as we are not ready to work on next major version of this module now. Sorry for inconveniences.