Revert exec -> build

Exec requires GUI launching, which can be a pain with Actions. Let's ignore this for now.

Author: MJVL

.github/workflows/maven.yml

@@ -17,7 +17,7 @@ jobs:
       uses: actions/setup-java@v1
       with:
         java-version: 1.8
-    - name: Exec
-      run: mvn compile exec:java
+    - name: Build
+      run: mvn -B package --file pom.xml
     - name: Package
       run: mvn package