Stop popper warning that map file doesn't exist

[Rebecca Blundell]

Currently the popper library is logging a warning that popper.min.js.map does not exist:

error.log.1:1172:[Fri Feb 14 13:50:53.397235 2020] [core:info] [pid 5090] [client 192.xxx.xxx.xx:50078] AH00128: File does not exist: <mahara_dir>/htdocs/js/popper/popper.min.js.map

access.log.1:7223:192.xxx.xxx.xx - - [17/Feb/2020:13:58:41 +1300] "GET //js/popper/popper.min.js?v=8673 HTTP/1.1" 200 7820 "http://<www_dir>/admin/extensions/pluginconfig.php?plugintype=search&pluginname=elasticsearch" "Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:73.0) Gecko/20100101 Firefox/73.0

I found this when configuring elasticsearch, but it is possible it is triggered on other occasions popper is used.

This seems to happen because the last line of htdocs/js/popper.min.js is:

//# sourceMappingURL=popper.min.js.map

Even though the line is commented out, it seems to trigger this warning that the map file doesn't exist. The map file is not required.

A quick fix is to remove the line entirely. We need to check it that is the best solution, however.