replace left shift operator with doLast block

the left shift operator is deprecated since Gradle 3.2 and was removed from Gradle 5. With the left shift operator, controlsfx will not build using Gradle 5.

build.gradle

@@ -74,8 +74,10 @@ subprojects {
     }
 
     // Used in Travis
-    task getVersion << {
-        println "$project.version"
+    task getVersion {
+        doLast {
+            println "$project.version"
+        }
     }
 
 }