fix(bake): regression missing cache on blog index
fix(bake): regression missing cache on blog index

Switched to _.memoize (probably less confusing in this instance).
Regression introduced: https://github.com/owid/owid-grapher/commit/2dd7f0661ba6fe7fdfb1ad2a59b9ef7ed7a2ad9f#diff-ab0604f7a26be8d1267ef4e5fcec2f3e4a321c61a83a763796ac0710b7cac81bL553

owid/owid-grapher,owid/owid-grapher,OurWorldInData/owid-grapher,owid/owid-grapher,OurWorldInData/owid-grapher,OurWorldInData/owid-grapher,OurWorldInData/owid-grapher,owid/owid-grapher,owid/owid-grapher,OurWorldInData/owid-grapher