update tests and ci starts from 5.4

[harikt]

@koriym Aura.Html is supporting from 5.3 onwards.

We cannot support 5.3 tests, yoast/polyfill only starts with 5.4 .

So without a CI we cannot support 5.3 and probably as a convenience we should update the composer.json php version to 5.4.0 so that only php versions that support will get installed. So no accidental damage. That may be considered as a BC break though.

[codecov-commenter]

Codecov Report

❗ No coverage uploaded for pull request base (2.x@c128f28). Click here to learn what that means.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             2.x       #61   +/-   ##
=======================================
  Coverage       ?   100.00%           
  Complexity     ?       227           
=======================================
  Files          ?        42           
  Lines          ?       863           
  Branches       ?         0           
=======================================
  Hits           ?       863           
  Misses         ?         0           
  Partials       ?         0           

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[harikt]

I am merging this. But please look into the comments on 5.3 and 5.4 .