Since the last release of this library was in 2013, I'd consider using jQuery noConflict in order to use both the new jQuery version and the old one that supports the library.
<script type="text/javascript" src="https://code.jquery.com/jquery-3.3.1.min.js"></script>
<!-- revert global jQuery and $ variables and store jQuery in a new variable -->
<script type="text/javascript">
var jQuery_3_3_1 = $.noConflict(true);
</script>
<!-- load jQuery 1.3.2 -->
<script type="text/javascript" src="http://code.jquery.com/jquery-1.3.2.js"></script>
<!-- revert global jQuery and $ variables and store jQuery in a new variable -->
<script type="text/javascript">
var jQuery_1_3_2 = $.noConflict(true);
</script>
This way you can keep your support for the ImageMapster but also use the updated jQuery.