Create .gradle dir before installation

Create .gradle directory to avoid errors when unpacking cached files (I hope this helps).

.abstruse.yml

@@ -3,6 +3,9 @@ image: openjdk
 matrix:
   - env: SCRIPT=shadowJar
 
+before_install:
+  - mkdir .gradle
+
 script:
   - if [[ "SCRIPT" ]]; then gradle $SCRIPT; fi