Improve unused CSS reporting

[arggh]

Would be nice, if I could get information on the file or component, where the unused CSS is.

Currently, this is what we get:

Module Warning (from ./node_modules/svelte-loader/index.js):
Unused CSS selector (148:2)
146:   }
147:
148:   .item img {
       ^
149:     width: 100%;
150:     height: 100%;

[Rich-Harris]

Try updating! This was fixed yesterday in #371

[arggh]

This was the fastest issue fix ever! Much better now, thanks!