Callback required in Node v10+

[nwittwer]

Hi, I'm running into an issue which looks like it's coming from using Node v10+:

Based on the search docs, I tried this in my Gulp file:

function docs() {
  return gulp.src('docs/**/*.md')
  .pipe( Super.init() )
    .on('finish', function() {
        Super.buildSearch('docs/sitemap.json');
    })
  .pipe(gulp.dest('dist'))
}

However, I get this error:

TypeError [ERR_INVALID_CALLBACK]: Callback must be a function
    at maybeCallback (fs.js:133:9)
    at Object.writeFile (fs.js:1132:14)
    at /Users/dev/UI-design-workspace/node_modules/supercollider/lib/buildSearch.js:62:8
    at /Users/dev/UI-design-workspace/node_modules/supercollider/node_modules/mkdirp/index.js:48:26
    at FSReqWrap.oncomplete (fs.js:159:5)

Version info:
Supercollider: ^1.4.4
Gulp: 4.0
Node: 10.6.0

Maybe an update is need for this library to support Node v10+? It looks like the callback() is no longer optional for the Super.buildSearch() function, since Node v10.0. (Open the History panel)

---

I played around with a few hotfixes:

1.) Changing the fs.writeFile to fs.writeFileSync. I don't think this is a good long-term solution, as it changes from async to synchronous file writing.

File: buildSearch.js, line 62
Current: fs.writeFile(outFile, JSON.stringify(results, null, ' '), cb);
Hotfix: fs.writeFile(outFile, JSON.stringify(results, null, ' '), cb);

2.) Adding an empty callback function in the Gulp task.

function docs() {
  return gulp.src('docs/**/*.md')
  .pipe( Super.init() )
    .on('finish', function() {
        Super.buildSearch( 'docs/sitemap.json', function(){} ); // <---- empty callback function
    })
  .pipe(gulp.dest('dist'))
}

P.S. Supercollider is still awesome. But I may be biased ;)

[kball]

I believe issues with node 10 and 12 have been resolved in #22. Tests work, and foundation can build.