partial update for svelte3

[Foxcapades]

Updated import for the new svelte 3 package structure.

Using this update in my current builds without issue.

G.task('compile-svelte', () => G.src('./src/**/*.svelte')
  .pipe(svelte({css: false, format: 'cjs'}))
  .pipe(G.dest(dirs.work)));

[08:27:29] Starting 'compile-svelte'...
[08:27:35] Finished 'compile-svelte' after 5.39 s

[coveralls]

Coverage remained the same at 100.0% when pulling bda72cd on Foxcapades:master into 791ab3f on shinnn:master.

[Foxcapades]

Omitted because the svelte compiler was throwing an error for the existence of the 'preprocess' entry in the options.

[criticalmash]

Hi, any reason why this has not merged? I have a site that I'd like to upgrade to Svelte 3.

Thanks