Add missing v prefix

Author: LouisCAD

RELEASING.md

@@ -7,7 +7,7 @@ file to a non-SNAPSHOT version.
 2. Update the `README.md` with the new version.
 3. Run `git commit -am "Prepare for release X.Y.Z"`
 (where X.Y.Z is the new version).
-4. `git tag -a X.Y.Z -m "Version X.Y.Z"` (where X.Y.Z is the new version).
+4. `git tag -a vX.Y.Z -m "Version X.Y.Z"` (where X.Y.Z is the new version).
 5. Run `./gradlew clean bintrayUpload`.
 6. Run `git push origin`.
 7. Sign in on Bintray and publish the packages.