Remove jcenter repository

[cd2357]

Replace the jcenter repo with mavenCentral and jitpack.

One of the dependencies had a slightly different name in jcenter compared to jitpack (com.github.jengelman.gradle.plugins:shadow vs com.github.johnrengelman:shadow), so that was renamed as well.

Fixes #5496

[ripcurlx]

utACK - as the lib hash hasn't been changed, so it should still be exact the same lib.

[cd2357]

I didn't find the shadow dependency hash in gradle-witness.gradle, maybe because its not a dependency per se but just a plugin used during building.

As a test, I updated the version to 6.0.0 in

bisq/build.gradle

Line 9 in ee6ccc4

classpath 'com.github.johnrengelman:shadow:5.2.0'

and gradle-witness didn't complain.

So the hash isn't checked.

I did find a way to preserve the plugin name (by adding another repo to the list, PR incoming).