Change OpenSearch to HTTPS

public/opensearch.xml

@@ -3,10 +3,10 @@
   <ShortName>DevDocs</ShortName>
   <Description>Search API documentation</Description>
   <Tags>devdocs</Tags>
-  <Url type="text/html" method="get" template="http://devdocs.io/#q={searchTerms}"/>
+  <Url type="text/html" method="get" template="https://devdocs.io/#q={searchTerms}"/>
   <Image height="16" width="16" type="image/vnd.microsoft.icon">https://cdn.devdocs.io/favicon.ico</Image>
   <Image height="64" width="64" type="image/x-icon">https://cdn.devdocs.io/images/icon-64.png</Image>
   <InputEncoding>UTF-8</InputEncoding>
-  <moz:SearchForm>http://devdocs.io</moz:SearchForm>
-  <Url type="application/opensearchdescription+xml" rel="self" template="http://devdocs.io/opensearch.xml"/>
+  <moz:SearchForm>https://devdocs.io</moz:SearchForm>
+  <Url type="application/opensearchdescription+xml" rel="self" template="https://devdocs.io/opensearch.xml"/>
 </OpenSearchDescription>