build: fix gradle script deprecations.

HMCL/build.gradle

@@ -123,7 +123,7 @@ shadowJar {
         attributes 'Created-By': 'Copyright(c) 2013-2020 huangyuhui.',
                 'Main-Class': mainClassName,
                 'Multi-Release': 'true',
-                'Implementation-Version': version,
+                'Implementation-Version': project.version,
                 'Class-Path': 'pack200.jar',
                 'Add-Opens': [
                         'java.base/java.lang',

HMCLTransformerDiscoveryService/build.gradle

@@ -7,6 +7,6 @@ dependencies {
 jar {
     manifest {
         attributes 'Created-By': 'Copyright(c) 2013-2020 huangyuhui.',
-                'Implementation-Version': version
+                'Implementation-Version': project.version
     }
 }

build.gradle

@@ -1,6 +1,6 @@
 buildscript {
     repositories {
-        jcenter()
+        mavenCentral()
         maven { url 'https://plugins.gradle.org/m2/' }
     }
 }
@@ -20,7 +20,6 @@ subprojects {
 
     repositories {
         mavenCentral()
-        jcenter()
 
         maven { url 'https://jitpack.io' }
     }