fixed "libpng warning: iCCP: known incorrect sRGB profile" error

=== before ===
(find . -iname '*.png' -type f -exec identify -verbose '{}' +) |& grep 'known incorrect sRGB profile'
identify: iCCP: known incorrect sRGB profile `./can-icon-24px-green.png' @ warning/png.c/MagickPNGWarningHandler/1830.
identify: iCCP: known incorrect sRGB profile `./greenicon.png' @ warning/png.c/MagickPNGWarningHandler/1830.
identify: iCCP: known incorrect sRGB profile `./can-icon-24px-yellow.png' @ warning/png.c/MagickPNGWarningHandler/1830.
identify: iCCP: known incorrect sRGB profile `./redicon.png' @ warning/png.c/MagickPNGWarningHandler/1830.
identify: iCCP: known incorrect sRGB profile `./can-icon-24px.png' @ warning/png.c/MagickPNGWarningHandler/1830.
identify: iCCP: known incorrect sRGB profile `./can-icon-24px-red.png' @ warning/png.c/MagickPNGWarningHandler/1830.
identify: iCCP: known incorrect sRGB profile `./can-icon-16px.png' @ warning/png.c/MagickPNGWarningHandler/1830.
identify: iCCP: known incorrect sRGB profile `./yellowicon.png' @ warning/png.c/MagickPNGWarningHandler/1830.