Fix Apache license version

[jspricke]

No description provided.

[ahcorde]

Changes LGTM but this should target ign-physics3

[codecov]

Codecov Report

Merging #325 (da23424) into ign-physics5 (abd7c45) will not change coverage.
The diff coverage is n/a.

@@              Coverage Diff              @@
##           ign-physics5     #325   +/-   ##
=============================================
  Coverage         75.73%   75.73%           
=============================================
  Files               129      129           
  Lines              5762     5762           
=============================================
  Hits               4364     4364           
  Misses             1398     1398           

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[jspricke]

this should target ign-physics3

Why? I found them while doing a code review of ign-physics5 for Debian. Also 5 is your default branch.

[chapulina]

this should target ign-physics3
Why?

Please refer to our contribution guidelines:

"Pull requests should target the lowest possible supported version where the changes can be added in a backwards-compatible way (no API / ABI / behavior break in released branches)."

If that's too much of a hassle for you, we can backport the PR after it's merged though.

You'll still need to sign your commit for the DCO checker though, thanks!

[jspricke]

Please refer to our [contribution guidelines](https://ignitionrobotics.org/docs/all/contributing#process): "_Pull requests should target the lowest possible supported version where the changes can be added in a backwards-compatible way (no API / ABI / behavior break in released branches)._"

That sounds uncommon, you may want to revisit how other projects doing it, i.e. backporting the changes.

If that's too much of a hassle for you, we can backport the PR after it's merged though.

Please do, for example `dartsim/src/WorldFeatures_TEST.cc` is not in ign-physics3, so I would need to fill more then one PR?

You'll still need to sign your commit for the DCO checker though, thanks!

Done.