fix for circle tag as new verion name (#158)

Author: thomaszurkan-optimizely

build.gradle

@@ -19,7 +19,7 @@
 buildscript {
     def bintray_user = System.getenv('BINTRAY_USER')
     def bintray_api_key = System.getenv('BINTRAY_API_KEY')
-    def version_name = System.getenv('TRAVIS_TAG')
+    def version_name = System.getenv('CIRCLE_TAG')
     if (bintray_user != null && bintray_api_key != null && version_name != null) {
         rootProject.ext.bintray_user = bintray_user
         rootProject.ext.bintray_api_key = bintray_api_key