Switch from JCenter to MavenCentral

JCenter has been sunset. See <https://jfrog.com/blog/into-the-sunset-bintray-jcenter-gocenter-and-chartcenter/>.

build.gradle

@@ -51,7 +51,7 @@ plugins {
 allprojects {
     repositories {
         google()
-        jcenter()
+        mavenCentral()
         maven {
             name "Mozilla"
             url "https://maven.mozilla.org/maven2"

settings.gradle

@@ -14,7 +14,7 @@ buildscript {
         classpath 'org.yaml:snakeyaml:2.2'
     }
     repositories {
-        jcenter()
+        mavenCentral()
     }
 }
 

tools/nimbus-gradle-plugin/build.gradle

@@ -19,7 +19,7 @@ gradlePlugin {
 
 repositories {
     google()
-    jcenter()
+    mavenCentral()
     maven {
         name "Mozilla"
         url "https://maven.mozilla.org/maven2"

tools/nimbus-gradle-plugin/settings.gradle

@@ -8,7 +8,7 @@ buildscript {
         classpath 'org.yaml:snakeyaml:2.2'
     }
     repositories {
-        jcenter()
+        mavenCentral()
     }
 }