fix www image demo #99

Job	Run time
build (release-v4.4, calibration_helper)	4m 1s
build (release-v4.4, demo)	3m 51s
build (release-v4.4, dragon)	3m 18s
build (release-v4.4, grayscale_test)	3m 13s
build (release-v4.4, mpd_status)	3m 19s
build (release-v4.4, terminal)	3m 50s
build (release-v4.4, www-image)	3m 30s
build (release-v5.1, calibration_helper)	3m 19s
build (release-v5.1, demo)	3m 34s
build (release-v5.1, dragon)	3m 14s
build (release-v5.1, grayscale_test)	3m 15s
build (release-v5.1, mpd_status)	4m 9s
build (release-v5.1, terminal)	3m 55s
build (release-v5.1, www-image)	3m 14s
build-arduino (release-v4.4, weather)	2m 5s
	51m 47s

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