Build issue with node 6

[Phyks]

Not really important, but there is a build issue with Node 6:

ERROR in ./~/css-loader?-svgo&-autoprefixer&-mergeRules!./~/postcss-loader!./~/stylus-loader!./app/styles/app.styl
Module build failed: TypeError: /tmp/cozy-music/app/styles/app.styl:86:1
   82| @import 'player'
   83| @import 'notification'
   84| @import 'dialog'
   85| @import 'playlists'
   86| 
-------^

Path must be a string. Received undefined

    at assertPath (path.js:7:11)
    at extname (path.js:1433:5)
    at new SourceMapper (/tmp/cozy-music/node_modules/stylus/lib/visitor/sourcemapper.js:41:7)
    at Renderer.render (/tmp/cozy-music/node_modules/stylus/lib/renderer.js:94:9)
    at /tmp/cozy-music/node_modules/stylus-loader/index.js:149:12
    at tryCatchReject (/tmp/cozy-music/node_modules/when/lib/makePromise.js:840:30)
    at runContinuation1 (/tmp/cozy-music/node_modules/when/lib/makePromise.js:799:4)
    at Fulfilled.when (/tmp/cozy-music/node_modules/when/lib/makePromise.js:590:4)
    at Pending.run (/tmp/cozy-music/node_modules/when/lib/makePromise.js:481:13)
    at Scheduler._drain (/tmp/cozy-music/node_modules/when/lib/Scheduler.js:62:19)
    at Scheduler.drain (/tmp/cozy-music/node_modules/when/lib/Scheduler.js:27:9)
    at _combinedTickCallback (internal/process/next_tick.js:67:7)
    at process._tickCallback (internal/process/next_tick.js:98:9)
 @ ./app/styles/app.styl 4:14-199

(Easy) fix is to update stylus-loader to latest version.