Bump to Gradle v4.4

Fixed according to google/ExoPlayer@13592df

Author: Roger Hu

Parse/build.gradle

@@ -69,10 +69,11 @@ android.libraryVariants.all { variant ->
 
     def javadoc = task("javadoc${variant.name.capitalize()}", type: Javadoc) {
         description "Generates Javadoc for $variant.name."
-        source = variant.javaCompile.source
+        source = variant.javaCompiler.source
         ext.androidJar = "${android.sdkDirectory}/platforms/${android.compileSdkVersion}/android.jar"
-        classpath = files(variant.javaCompile.classpath.files) + files(ext.androidJar)
-
+        doFirst {
+            classpath = files(variant.javaCompiler.classpath.files) + files(ext.androidJar)
+        }
         options.docletpath = [rootProject.file("./gradle/ExcludeDoclet.jar")]
         options.doclet = "me.grantland.doclet.ExcludeDoclet"
 

gradle/wrapper/gradle-wrapper.properties

@@ -3,4 +3,4 @@ distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-4.1-all.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-4.4-all.zip