Drop alpha channel to work with Pillow >4.2 (fixes #455).
Drop alpha channel to work with Pillow >4.2 (fixes #455).

psteph801/psteph801.github.io,mpetroff/pannellum,psteph801/psteph801.github.io,mpetroff/pannellum,psteph801/psteph801.github.io,mpetroff/pannellum,psteph801/psteph801.github.io,mpetroff/pannellum