update target gradle to 5.0 and matching kotlin dsl version

build.gradle

@@ -71,7 +71,7 @@ task createClasspathManifest {
 dependencies {
     compileOnly gradleApi()
     compileOnly localGroovy()
-    compileOnly "org.gradle:gradle-kotlin-dsl:1.0.3"
+    compileOnly "org.gradle:gradle-kotlin-dsl:1.0.4"
 
     compile 'com.google.guava:guava:18.0'
     compile 'com.google.gradle:osdetector-gradle-plugin:1.4.0'
@@ -86,7 +86,7 @@ dependencies {
     }
     testCompile 'commons-io:commons-io:2.5'
 
-    testProjectRuntime "org.jetbrains.kotlin:kotlin-gradle-plugin:1.3.10"
+    testProjectRuntime "org.jetbrains.kotlin:kotlin-gradle-plugin:1.2.0"
 
     // Add android plugin to the test classpath, so that we can jump into class definitions,
     // read their sources, set break points, etc while debugging android unit tests.

examples/exampleKotlinDslProject/gradle/wrapper/gradle-wrapper.properties

@@ -1,5 +1,5 @@
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-5.0-rc-3-bin.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-5.0-bin.zip
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists

src/test/groovy/com/google/protobuf/gradle/ProtobufKotlinDslPluginTest.groovy

@@ -9,7 +9,7 @@ import spock.lang.Specification
  * Unit tests for kotlin dsl extensions.
  */
 class ProtobufKotlinDslPluginTest extends Specification {
-  private static final List<String> GRADLE_VERSIONS = ["5.0-rc-3"]
+  private static final List<String> GRADLE_VERSIONS = ["5.0"]
 
   void "testProjectKotlinDsl should be successfully executed (java-only project)"() {
     given: "project from testProjectKotlinDslBase"