Uses BINTRAY_{USER,KEY} from env to upload/publish

Those two environment variables are set in the Travis settings.  They
will not appear in the output log, but can be used on command lines and
inside scripts as exported variables.

Author: Azhrei

.travis.yml

@@ -3,7 +3,7 @@
 # Or maybe the upload should always happen, but the publishing
 # is a separate task?
 language: java
-script: gradle build
+script: gradle build -Dpublish=true "-Duser=$BINTRAY_USER" "-Dkey=$BINTRAY_KEY"
 jdk:
 - oraclejdk8
 notifications:

build.gradle

@@ -159,13 +159,13 @@ publishing {
 bintray {
     user = System.getProperty('bintray.user')
     key = System.getProperty('bintray.key')
+    String publishProperty = System.getProperty('publish')
     publications = ['bintrayPublication']
 
     //Whether to run this as dry-run, without deploying
     dryRun = false
 
     //Whether version should be auto published after an upload
-    String publishProperty = System.getProperty('publish')
     publish = (publishProperty == "true")
     println "Publishing uploaded files:  " + publish