Fix gradle publish config to match Google docs. (#279)

gradle/gradle-publish.gradle

@@ -1,61 +1,57 @@
 apply plugin: 'maven-publish'
 apply plugin: 'signing'
 
-
 ext["signing.keyId"] = System.getenv('SIGNING_KEY_ID') ?: ''
 ext["signing.password"] = System.getenv('SIGNING_KEY_PASSWORD') ?: ''
 ext["signing.secretKeyRingFile"] = System.getenv('SIGNING_KEY_FILE') ?: ''
 
-afterEvaluate {
+android {
     publishing {
-        publications {
-            release(MavenPublication) {
-                groupId group
-                version project.ext.version
-                artifactId project.ext.name
+        singleVariant('release') {
+            withSourcesJar()
+        }
+    }
+}
+
+publishing {
+    publications {
+        release(MavenPublication) {
+            groupId group
+            version project.ext.version
+            artifactId project.ext.name
+
+            afterEvaluate {
                 from components.release
-                artifact androidSourcesJar //TODO: add javadocs
+            }
 
-                pom {
-                    name = project.ext.pom_name ?: ''
-                    packaging = POM_PACKAGING
-                    description = project.ext.pom_desc ?: ''
-                    url = POM_URL
-                    licenses {
-                        license {
-                            name = POM_LICENCE_NAME
-                            url = POM_LICENCE_URL
-                        }
+            pom {
+                name = project.ext.pom_name ?: ''
+                packaging = POM_PACKAGING
+                description = project.ext.pom_desc ?: ''
+                url = POM_URL
+                licenses {
+                    license {
+                        name = POM_LICENCE_NAME
+                        url = POM_LICENCE_URL
                     }
-                    developers {
-                        developer {
-                            id = POM_DEVELOPER_ID
-                            name = POM_DEVELOPER_NAME
-                            email = POM_DEVELOPER_EMAIL
-                        }
-                    }
-                    scm {
-                        connection = POM_SCM_CONNECTION
-                        developerConnection = POM_SCM_DEV_CONNECTION
-                        url = POM_SCM_URL
+                }
+                developers {
+                    developer {
+                        id = POM_DEVELOPER_ID
+                        name = POM_DEVELOPER_NAME
+                        email = POM_DEVELOPER_EMAIL
                     }
                 }
+                scm {
+                    connection = POM_SCM_CONNECTION
+                    developerConnection = POM_SCM_DEV_CONNECTION
+                    url = POM_SCM_URL
+                }
             }
         }
     }
 
     signing {
-        sign publishing.publications
-        sign configurations.archives
+        sign publishing.publications.release
     }
 }
-
-task androidSourcesJar(type: Jar) {
-    archiveClassifier.set('sources')
-    from android.sourceSets.main.java.srcDirs
-    from android.sourceSets.main.kotlin.srcDirs
-}
-
-artifacts {
-    archives androidSourcesJar
-}