easy gitlab-ci with fdroid nightly support

Update .gitlab-ci

.gitlab-ci.yml

+image: registry.gitlab.com/fdroid/ci-images-client:latest
+
+cache:
+  paths:
+    - .gradle/wrapper
+    - .gradle/caches
+
+stages:
+  - build
+
+before_script:
+  - apt-get -qy  install gradle
+  - export GRADLE_USER_HOME=$PWD/.gradle
+  - export ANDROID_COMPILE_SDK=`sed -n 's,.*compileSdkVersion\s*\([0-9][0-9]*\).*,\1,p' app/build.gradle`
+  - echo y | sdkmanager "platforms;android-${ANDROID_COMPILE_SDK}" > /dev/null
+
+build:
+  stage: build
+  except:
+  - develop
+  script:
+  - ./gradlew
+  artifacts:
+    paths:
+    - build/outputs/
+
+publish:
+  stage: build
+  only:
+  - develop
+  script:
+  # generate new version
+  - export versionCode="$CI_JOB_ID"
+  - export versionName="$(git describe --tag --abbrev=0)-${CI_JOB_ID}_${CI_COMMIT_REF_NAME}"
+  - echo "set VersionCode '${versionCode}' and VersonName '${versionName}'"
+  - sed -i "s/^\(\s*versionCode\s*\).*$/\1$versionCode/" app/build.gradle
+  - sed -i "0,/versionName/s/^\(\s*versionName\).*/\1 \"$versionName\"/" app/build.gradle
+  - cat -n app/build.gradle
+  # build free version
+  - ./gradlew
+  # publish on nightly fdroid repo
+  - fdroid nightly -v
+
+after_script:
+  # this file changes every time but should not be cached
+  - rm -f $GRADLE_USER_HOME/caches/modules-2/modules-2.lock
+  - rm -fr $GRADLE_USER_HOME/caches/*/plugin-resolution/