Update references to w3c.org content to use HTTPS (w3c#63)

Take advantage of w3c.org serving over HTTPS already.

index.src.html

@@ -35,12 +35,12 @@ <h1>Content Security Policy Level 3</h1>
     text: eval(); url: sec-eval-x
     text: Function(); url: sec-function-objects
     text: JSON.stringify(); url: sec-json.stringify
-spec: DOM; urlPrefix: http://www.w3.org/TR/dom/
+spec: DOM; urlPrefix: https://www.w3.org/TR/dom/
   type: interface
     text: Element; url: interface-element
   type: attribute
     text: textContent; for: Node; url: dom-node-textcontent
-spec: HTML5; urlPrefix: http://www.w3.org/TR/html5/
+spec: HTML5; urlPrefix: https://www.w3.org/TR/html5/
   type: dfn
     urlPrefix: embedded-content-0.html
       text: an iframe srcdoc document
@@ -160,7 +160,7 @@ <h1>Content Security Policy Level 3</h1>
       text: integrity metadata; url: concept-request-integrity-metadata
   type: interface
     text: Request
-spec: MIX; urlPrefix: http://www.w3.org/TR/mixed-content/
+spec: MIX; urlPrefix: https://www.w3.org/TR/mixed-content/
   type: dfn; text: block-all-mixed-content
 spec: URL; urlPrefix: https://url.spec.whatwg.org/
   type: dfn
@@ -179,13 +179,13 @@ <h1>Content Security Policy Level 3</h1>
     text: scheme; for: URL; url: concept-url-scheme
   type: interface;
     text: URL
-spec: SERVICE-WORKERS; urlPrefix: http://www.w3.org/TR/service-workers/
+spec: SERVICE-WORKERS; urlPrefix: https://www.w3.org/TR/service-workers/
   type: interface
     text: ServiceWorker; url: service-worker-interface
-spec: WORKERS; urlPrefix: http://www.w3.org/TR/workers/
+spec: WORKERS; urlPrefix: https://www.w3.org/TR/workers/
   type: interface
     text: Worker
-spec: CSSOM; urlPrefix: http://www.w3.org/TR/cssom/
+spec: CSSOM; urlPrefix: https://www.w3.org/TR/cssom/
   type: dfn
     text: insert a css rule
     text: parse a css declaration block
@@ -255,7 +255,7 @@ <h1>Content Security Policy Level 3</h1>
   },
   "HTML-DESIGN": {
     "authors": [ "Anne Van Kesteren", "Maciej Stachowiak" ],
-    "href": "http://www.w3.org/TR/html-design-principles/",
+    "href": "https://www.w3.org/TR/html-design-principles/",
     "title": "HTML Design Principles",
     "publisher": "W3C"
   },