Target sdk 28

[naXa777]

I've already done this in my fork. Take a look at these commits for reference:

• https://github.com/naXa777/SoundRecorder/commit/3d5eae7548c28ca83eaa38de37203f7502e03442
• https://github.com/naXa777/SoundRecorder/commit/0948810aad6add3924060dc47c9997a42db559df
• https://github.com/naXa777/SoundRecorder/commit/04576fbef42bd5c1add97005a45b317f7f4e64bb