Adding support for php 7.3 and 7.4 in branch 3.6

[ishyevandro]

No description provided.

[alcaeus]

@ishyevandro if you rebase your branch the build should be stable. Note that you may have to rename the upstream remote to whatever you use locally:

git fetch upstream
git rebase upstream/3.6
git push --force

[ishyevandro]

@alcaeus, fixed.