Ans1) I just moved src="js/libs/modernizr-2.5.3-respond-1.1.0.min.js" in scripts section to load when other scripts are being loaded. Its not a replacement to src="//code.jquery.com/jquery-1.11.2.min.js". modernizr plugin is not a part of jquery. So we cannot remove that plugin.
Ans2) If there is no protocol specfied before the src, then browser uses the same protocol which is used for loading that html file (http or https).
So, its okay to not specify protocol and the code still works in any case.
Fixed console log errors which were appearing due to migration of Jquery from 1.1 to 3.3.1 version.