[SKIP CI] fix env var handling

.drone.yml

@@ -7,13 +7,12 @@ steps:
     image: xoxys/rpmbuild
     pull: always
     environment:
-      RELEASE: "${DRONE_TAG##v}"
-      CUPSRELEASE: "${RELEASE:-2.2.10}"
+      CUPSRELEASE: "${DRONE_TAG##v}"
     commands:
-      - echo $CUPSRELEASE
-      - wget https://github.com/apple/cups/releases/download/v${CUPSRELEASE:-2.2.10}/cups-${CUPSRELEASE:-2.2.10}-source.tar.gz
+      - [ -z "$var" ] && CUPSRELEASE=2.2.10
+      - wget https://github.com/apple/cups/releases/download/v$CUPSRELEASE/cups-$CUPSRELEASE-source.tar.gz
       - mkdir ./rpms
-      - rpmbuild -ta --define "_rpmdir $(pwd)/rpms" --without libusb1 cups-${CUPSRELEASE:-2.2.10}-source.tar.gz
+      - rpmbuild -ta --define "_rpmdir $(pwd)/rpms" --without libusb1 cups-$CUPSRELEASE-source.tar.gz
     when:
       event:
         - push