Remove minus from appDef to align to TS configuration

src/main/resources/config/application-theia.yml

@@ -6,7 +6,7 @@ theia:
         # Upper level key is the language category (must match the language key in the programming-exercise configuration)
         java:
             # Lower level key can be multiple flavors of the image, e.g. version, tag, or additional dependencies
-            Java-17: "my-registry/my-image:my-tag"
+            java17: "my-registry/my-image:my-tag"
             # Add more flavors here (e.g. Java-11, Java-8, etc.)
         # Add more languages here (e.g. c, python, etc.)
         c: