Fix: relative paths in @import statements don't work.

Previous attempts to allow relative paths in @import statements added
to `sassOptions.includePaths`. That was deemed unacceptable as it would
capture relative files that weren't explicitly imported with relative paths.

The solution is to pass the filename in `sassOptions`. It's fine to pass
the javascript file path: we are already providing the `data` option with
the content to parse, so sass won't actually try to read the file. It is only
used for resolving explicit relative imports.

Author: jamestalmage

index.js

@@ -14,9 +14,11 @@ module.exports = (css, settings) => {
   const optionData = settings.sassOptions && settings.sassOptions.data || "";
   const data = optionData + "\n" + cssWithPlaceholders;
 
+  const file = settings.babel && settings.babel.filename;
+
   const preprocessed = sass.renderSync(
     Object.assign(
-      {},
+      {file},
       settings.sassOptions,
       { data }
     )).css.toString()

test.js

@@ -122,9 +122,6 @@ describe('styled-jsx-plugin-sass', () => {
 
     assert.equal(
       plugin(file.toString(), {
-        sassOptions: {
-          includePaths: [path.join(__dirname, 'fixtures')]
-        },
         babel: { filename }
       }).trim(),
       cleanup(`