Fixed bintrayUpload plugin for latest Gradle & AGP version.

Author: Piotr Zawadzki

build.gradle

@@ -4,7 +4,7 @@ buildscript {
     ext.KOTLIN_VERSION = '1.3.41'
     ext.ANDROID_GRADLE_PLUGIN_VERSION = '3.5.0'
     ext.DOKKA_VERSION = '0.9.17'
-    ext.BINTRAY_VERSION = '1.7.3'
+    ext.BINTRAY_VERSION = '1.8.4'
     repositories {
         google()
         jcenter()