[CSS] Don’t combine multiple selectors onto same line

[keithjgrant]

Right now, Prettier merges multiple selectors into the same line if space allows:

.foo,
.bar,
.baz {}

becomes:

.foo, .bar, .baz {}

I don’t think this behavior jives with the way most people write CSS. It is both my preference and, I think, more common to always separate selectors onto their own lines, regardless of length. This helps when scanning a file visually for a particular selector, so .foo, .bar isn’t mis-read as .foo .bar.

Additional support for this reasoning: reading through the Bootstrap source, they keep selectors separate, regardless of length, in almost every instance. The Foundation framework also follows this practice for the most part, though it’s a little less consistent.

[keithjgrant]

BTW, thanks for the CSS support. This is awesome! 😃

[vjeux]

I just merged @yuchi's PR to fix this! #2047 In the next release of prettier it'll always print them line by line.