Videos with uppercase extension not recognized

First off, thanks for developing this tool, it's been really helpful.

I've got one issue so far though: When dealing with .MP4 files (as generated by many digital cameras), vue coolbox won't recognize it as a video. Looking at the code (

vue-cool-lightbox/src/components/CoolLightBox.vue

Line 1751 in 298d8ee

checkIsMp4(url) {

) it seems that currently the comparison is done in a case-sensitive way. Maybe changing this to be case insensitive would help solve this.