Fix issue with incorrect -DEV suffix in release.

The elvis operator returns the alternate branch if the condition is an empty string:

```groovy
groovy:000> "" ?: "pouet"
===> pouet

```

build.gradle

@@ -22,7 +22,7 @@ version = '8.0'
 ext {
     // Development_stage (DEV:0  BETA:1  STABLE:2)
     development_stage = project.properties['DEV_STAGE'] as Integer ?: 0
-    version_type = ["-DEV", "-BETA", ""].get(development_stage) ?: '-DEV'
+    version_type = ["-DEV", "-BETA", ""].get(development_stage)
     target_dir = "${buildDir}/artefacts"
 }