[css-values-5] 各種更新

Move "exploratory draft" issue from *progress() to *mix()
w3c/csswg-drafts@1bce33b

I a whole word
w3c/csswg-drafts@4f6a33f

Fix typos in early-resolution example
w3c/csswg-drafts@9d38c62

All participants in a cycle become invalid
w3c/csswg-drafts@e6147ce

Remove chapter on attr() cycles
w3c/csswg-drafts@5b45457

Use "include" when fetching cross-origin CSS resources
w3c/csswg-drafts@fc52569

Author: triple-underscore