So you don’t need that particular include.
Looking at the libraries tab in the webIDE, something is strange in that the library in github looks like it does not include that file but the one in the webIDE. This probably means that the published version is just behind the latest github version and checking on that the version the web is 0.0.1 while the github has 0.0.31.
Perhaps it just needs to be updated by the github owner “beefbowl”. You can leave an issue at github for him to republish. Just click the little cat head next the library name or you can try email at email@example.com.
As a work-around you can copy the files into the web IDE by clicking the little circle plus in the upper right–then you can edit the files if you need to. Github lets download a zip archive of the files if you want to.
I also have a ported Adafruit_LEDBackpack library on my github here. This was the time before there were libraries available in the webIDE and I never put them in the right format for that since I thought it was covered. I know these were working when I last tried them.