Correct request's "early-hints" initiator type

It has a trailing s.

Author: yoavweiss

fetch.bs

@@ -1633,7 +1633,7 @@ processing requirements.
 "<code>beacon</code>",
 "<code>body</code>",
 "<code>css</code>",
-"<code>early-hint</code>",
+"<code>early-hints</code>",
 "<code>embed</code>",
 "<code>fetch</code>",
 "<code>font</code>",