It's hardcoded in /library/XenForo/Dependenices/Public.php
A template edit alternative.
	
	
	
		Rich (BB code):
	
	
		<xen:if is="{$xenOptions.jQuerySource} == 'jquery'">
    <xen:set var="$jQuerySource">//code.jquery.com/jquery-1.10.1.min.js</xen:set>
</xen:if>
    <script src="{$jQuerySource}"></script>  
    <xen:if is="{$jQuerySource} != {$jQuerySourceLocal}">
        <script>if (!window.jQuery) { document.write('<scr'+'ipt type="text/javascript" src="{$jQuerySourceLocal}"><\/scr'+'ipt>'); }</script>
    </xen:if><xen:if is="{$xenOptions.uncompressedJs} == 1 OR {$xenOptions.uncompressedJs} == 3">
    <script src="{$javaScriptSource}/jquery/jquery.xenforo.rollup.js?_v={$xenOptions.jsVersion}"></script></xen:if>  
    <script src="{xen:helper javaScriptUrl, '{$javaScriptSource}/xenforo/xenforo.js?_v={$xenOptions.jsVersion}'}"></script>
<!--XenForo_Require:JS-->
	 
 
If the source is set to jQuery it uses the // prefix which should work on either http or https.