Use HTTPS URLs for embedded images.

wiki/src/blueprint/translation_platform.mdwn

@@ -82,8 +82,8 @@ more information.
 There are several languages enabled and users can suggest translations
 in several languages:
 
-<a href="http://translate.tails.boum.org/engage/tails/?utm_source=widget">
-<img src="http://translate.tails.boum.org/widgets/tails/-/multi-red.svg" alt="Translation status" />
+<a href="https://translate.tails.boum.org/engage/tails/?utm_source=widget">
+<img src="https://translate.tails.boum.org/widgets/tails/-/multi-red.svg" alt="Translation status" />
 </a>
 
 What we plan to do is: