snipper-chosser.js may be incompatible with wagtail 2.11.1

[brookzhcn]

I upgraded wagtail to 2.11.1 and found it can't open snipper chooser modal in admin.I found that snipper-chosser.js is not same with the official one. This could be a upgrade isssue.

[murray3k]

Yes wagtail changed where the snipper chooser gets it URL from. I provided a small fix for this see: #69 .

[roodie]

With the latest wagtail version (2.12) the page-chooser.js also causing errors unfortunately.