Switch to Maven Central from JCenter, which is shutting down

https://jfrog.com/blog/into-the-sunset-bintray-jcenter-gocenter-and-chartcenter/

build.gradle

@@ -21,7 +21,7 @@ wrapper {
 }
 
 repositories {
-	jcenter()
+	mavenCentral()
 	if (isSnapshot) {
 		maven {
 			name("Sonatype snapshots")