fix(font-family): use sans-serif instead of sans

[JLHwung]

sans is not a valid generic font-family, see https://www.w3.org/TR/CSS2/fonts.html#generic-font-families

[sofish]

im not trying to develop a tool that valid but to make a website looks better

thanks

[JLHwung]

I am wondering why using sans here will make a website looks better since sans is not valid generic font family and the browser will simply ignore this value. If so, sans should be deleted.

[sofish]

not because of sans or sans-serif but the whole lib,
pull-request that makes a website looks better will be merged but not one that makes valid

[JLHwung]

After browsing on the history I found that sans-serif was replaced by sans in 5c96950, could you explain why sans-serif should be replaced by sans here? Is it related to any WebKit bugs? Thank you.

[sofish]

after a review, i think you are right on this
thanks, again

[JLHwung]

You are very welcome.