core: Upgrade to Gradle 6.8.3

Author: ChristopheCVB

build.gradle

@@ -21,10 +21,7 @@ java.sourceCompatibility = JavaVersion.VERSION_1_8
 
 repositories {
     mavenLocal()
-    jcenter()
-    maven {
-        url = uri('https://repo.maven.apache.org/maven2/')
-    }
+    mavenCentral()
 }
 
 dependencies {

gradle/wrapper/gradle-wrapper.properties

@@ -1,5 +1,5 @@
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-6.7.1-bin.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-6.8.3-bin.zip
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists