[Java] Add build script repositories.

Author: mjpt777

build.gradle

@@ -13,6 +13,12 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
+buildscript {
+    repositories {
+        mavenCentral()
+    }
+}
+
 plugins {
     id 'java'
     id 'com.github.johnrengelman.shadow' version '2.0.2' apply false