Use protocol-relative image url in welcome.json

website/static/welcome/welcome.json

@@ -7,7 +7,7 @@
 		"startDate":"1888",
 		"text": "<p>TimelineJS is an open-source tool that enables you to build visually-rich interactive timelines and is available in 40 languages.</p><p>You're looking at an example of one right now.</p><p>Click on the arrow to the right to learn more.</p>",
 		"asset": {
-			"media":"http://2.bp.blogspot.com/-dxJbW0CG8Zs/TmkoMA5-cPI/AAAAAAAAAqw/fQpsz9GpFdo/s1600/voyage-dans-la-lune-1902-02-g.jpg",
+			"media":"//2.bp.blogspot.com/-dxJbW0CG8Zs/TmkoMA5-cPI/AAAAAAAAAqw/fQpsz9GpFdo/s1600/voyage-dans-la-lune-1902-02-g.jpg",
 			"credit":"",
 			"caption":""
 		},