Fix missing context for prometheus exporter push

CircleCI will only share context if the requirements are correct, this
adds a missing requirement in the chain in order to push the images at
the end.

Author: renatomefi

.circleci/config.yml

@@ -21,6 +21,7 @@ version: 2.1
         - build-http
         - build-fpm
         - build-cli
+        - build-prometheus-exporter-file
   - test-http-e2e: *test-http
   - test-prometheus-exporter-file-e2e: &test-prometheus-exporter-file-e2e
       requires: