Compatibility with sass-loader v9

[Thibaud-R]

The sass-loader v9 and its new syntax for prependData is not taken in account in vue-cli-plugins v0.0.7.

Line 100 of index.js should be:
// Merge with user-defined loader data config
if (sassLoaderVersion < 8) opt.data = variables
else if (sassLoaderVersion < 9) opt.prependData = variables
else opt.additionalData = variables

All preset failed to compil, without the last 2 lines.

[Thibaud-R]

Sorry duplicate and already manage in the PR pull #185