+ picturefill v1.2.1

Though v2 branch is more updated, a [v1 branch is maintained](https://github.com/scottjehl/picturefill/tree/master#picturefill) since it acts differently.
Changes to source: "` v1.2.1`"
Merge pull request #1651 from tomByrer/patch-5

+ picturefill v1.2.1