Update dokka [0.9.18->0.10.0], fix Java API links (point to website).

Author: greenrobot-team

objectbox-kotlin/build.gradle

@@ -4,7 +4,7 @@ version= rootProject.version
 buildscript {
     ext.javadocDir = "$buildDir/docs/javadoc"
     ext.kotlin_version = '1.3.31'
-    ext.dokka_version = '0.9.18'
+    ext.dokka_version = '0.10.0'
 
     repositories {
         mavenCentral()
@@ -25,6 +25,17 @@ sourceCompatibility = 1.7
 dokka {
     outputFormat = 'html'
     outputDirectory = javadocDir
+
+    // Fix "Can't find node by signature": have to manually point to dependencies.
+    // https://github.com/Kotlin/dokka/wiki/faq#dokka-complains-about-cant-find-node-by-signature-
+    configuration{
+        externalDocumentationLink {
+            // Point to web javadoc for objectbox-java packages.
+            url = new URL("https://objectbox.io/docfiles/java/current/")
+            // Note: Using JDK 9+ package-list is now called element-list.
+            packageListUrl = new URL(url, "element-list")
+        }
+    }
 }
 
 task javadocJar(type: Jar, dependsOn: dokka) {