message: improve comment grammar
diff: @@ -24,7 +24,7 @@ clone() {
  # Try the PR author's branch in case it exists on the deps as well.
  # First we check if GITHUB_HEAD_REF is defined,
  # Then we check if BUILDKITE_BRANCH is defined,
  -# if it isn't we can assume this is a Netlify build
  +# if they aren't we can assume this is a Netlify build
  if [ -n "$GITHUB_HEAD_REF" ]; then
  head=$GITHUB_HEAD_REF
  elif [ -n "$BUILDKITE_BRANCH" ]; then
  