[CUSTOM_APP] Correctly set the version_name.

The version_name need to be set a compilation time.
By default the version_name is taken from json info file.
But a user may want to change it.

travis/make_release.sh

@@ -22,7 +22,6 @@ ${TRAVIS_BUILD_DIR}/build_custom_app.py \
   --custom-app ${CUSTOM_APP} \
   --package-name ${PACKAGE_NAME} \
   --google-api-key ${GOOGLE_API_KEY} \
-  --version ${VERSION} \
   --zim-url ${ZIM_URL} \
   --apks-dir ${HOME}/APKS \
   --content-version-code ${CONTENT_VERSION_CODE}