Set repository build version (Fixes #496)

Author: jaydrogers

src/variations/unit/Dockerfile

@@ -140,6 +140,9 @@ RUN docker-php-serversideup-dep-install-alpine "${DEPENDENCY_PACKAGES_ALPINE}" &
     chown -R www-data:www-data /var/www && \
     chmod -R 755 /var/www && \
     \
+    # Set the image version
+    echo "${REPOSITORY_BUILD_VERSION}" > /etc/serversideup-php-version && \
+    \
     # Make composer cache directory
     mkdir -p "${COMPOSER_HOME}" && \
     chown -R www-data:www-data "${COMPOSER_HOME}" && \