[Editorial] Fix link to published CSP 2 (#606)

Author: bwbroersma

README.md

@@ -3,6 +3,6 @@ Content Security Policy
 
 CSP 3 is being specified in `index.bs` (published at <https://www.w3.org/TR/CSP3/>)
 
-CSP 2 is published as a CR at <https://w3c.org/TR/CSP2>.
+CSP 2 is published as a CR at <https://www.w3.org/TR/CSP2/>.
 
 CSP 1 is published as a Note at <https://www.w3.org/TR/2012/CR-CSP-20121115/>