Fix Nexus build step

[benjaminoakes]

Background

ci/circleci: gem-publish-1 currently fails

Proposed

Fix the error so that this step can complete successfully

Notes

Related: #38 (comment)

Nexus | Check if version is already present in the repository

#!/bin/bash -eo pipefail
gem list --prerelease --all --remote --clear-sources \
  --source https://${NEXUS_PUSH_USER}:${NEXUS_PUSH_PASS}@${NEXUS_URL} \
  `cat gem/name` \
  | grep --invert-match "[( ,]`cat gem/version`[, )]"

ERROR:  While executing gem ... (NoMethodError)
    undefined method `downcase' for nil:NilClass

Exited with code exit status 1

CircleCI received exit code 1

[benjaminoakes]

As of right now, super_spreader may have to be manually pushed to RubyGems until changes to our CI pipeline for releasing open-source gems can be completed.