use file instead of content.

[KaboomFox]

Fixes false positive for characters in sass files that renderSync has issues parsing.

In node-sass

if (options.data) {
    status = binding.renderSync(options);
  } else if (options.file) {
    status = binding.renderFileSync(options);

renderSync has issues with some characters and errors with:

  at FSReqWrap.readFileAfterClose [as oncomplete] (fs.js:408:3)
        status: 1,
        file: 'stdin',
        line: 1,
        column: 9,
        message: 'returned value of `file` must be a string',
        formatted: 'Error: returned value of `file` must be a string\n        on line 1 of stdin\n>> @import "~react-vis/dist/main.scss";\n\n   --------^\n' 

By changing it to read the file instead it avoids this issue.

[KaboomFox]

Sorry I didn't get this in in-time for the release this morning!

[codecov]

Codecov Report

Merging #324 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master    #324   +/-   ##
======================================
  Coverage    98.4%   98.4%           
======================================
  Files          32      32           
  Lines         563     563           
======================================
  Hits          554     554           
  Misses          9       9

Impacted Files	Coverage Δ
src/parser/sass.js	100% <ø> (ø)	⬆️

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[rumpl]

Thanks! I'll wait some more this time for a release :)