Simplify GRADLE_USER_HOME setting in .gitlab-ci.yml

.gitlab-ci.yml

@@ -6,15 +6,13 @@ stages:
 
 variables:
   GRADLE_OPTIONS: --no-daemon --info --stacktrace --warning-mode=all
+  GRADLE_USER_HOME: "$CI_PROJECT_DIR/.gradle"
 
 cache:
   paths:
     - .gradle/wrapper
     - .gradle/caches
 
-before_script:
-  - export GRADLE_USER_HOME=`pwd`/.gradle
-
 tests:
   stage: test
   script: ./gradlew ${GRADLE_OPTIONS} check