CI: grep -v for exactly, not almost, the thing we insert #nitpick
Like, that's why we're `grep -v`-ing, may as well be precise
diff --git a/circle.yml b/circle.yml
index a1f419f..35eaeff 100644
--- a/circle.yml
+++ b/circle.yml
@@ -185,7 +185,7 @@
curl $(curl https://circleci.com/api/v1/project/mathquill/mathquill/latest/artifacts \
| $json -a url pretty_path -d '\n\t' \
| grep '\.png$' \
- | grep -v 'PREV' \
+ | grep -v 'PREV_' \
| sed "s:\$CIRCLE_ARTIFACTS/imgs/:-o $img_dir/PREV_:")
# Generate image diffs.
