More strict php dependency

[siemendev]

Hi folks,
as we learned from #16 (comment), It's extremely risky to depend on "php": ">=7.0.0" since there may be changes in future php versions that (once again) stop this lib from working although composer says that it works with the installed php version.

I suggest "php": "^7.0|^8.0" (adding the 8.0 assuming #17 has been merged by the time this issue is viewed).

Great work guys, keep it up :-)

[voku]

The problem is (I think) that composer will install an old version in this case. 😑

I was jung and thought I will maintain the lib anyway, so I don't need to use strict php versions. But in the meantime I switched the job, became 2x dad... how the time flies.