Doesn't build on Linux

Installed the latest yarn, stuff seems broken.

[13:34:44] मanishearth@aperture ~/mozilla/playpen/ui/frontend ^_^ 
$ yarn
yarn install v1.3.2
[1/4] Resolving packages...
[2/4] Fetching packages...
[########################################################################################-----------------------------------------------------] 477/[##########################################################################################---------------------------------------------------] 489/info fsevents@1.1.3: The platform "linux" is incompatible with this module.
info "fsevents@1.1.3" is an optional dependency and failed compatibility check. Excluding it from installation.
[3/4] Linking dependencies...
[4/4] Building fresh packages...
Done in 19.06s.
[13:35:06] मanishearth@aperture ~/mozilla/playpen/ui/frontend ^_^ 
$ yarn run watch
yarn run v1.3.2

/home/manishearth/mozilla/playpen/ui/frontend/webpack.config.js:115
  );
  ^

SyntaxError: Unexpected token )
    at createScript (vm.js:56:10)
    at Object.runInThisContext (vm.js:97:10)
    at Module._compile (module.js:542:28)
    at Object.Module._extensions..js (module.js:579:10)
    at Module.load (module.js:487:32)
    at tryModuleLoad (module.js:446:12)
    at Function.Module._load (module.js:438:3)
    at Module.require (module.js:497:17)
    at require (internal/module.js:20:19)
    at requireConfig (/home/manishearth/mozilla/playpen/ui/frontend/node_modules/webpack/bin/convert-argv.js:97:18)
error Command failed with exit code 1.
info Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.

Start with ui/frontend/webpack.config.js around line 115 and reproduce the reported failure by running yarn install followed by yarn run watch on Linux. Determine why the configuration produces the SyntaxError, then verify that the watch command starts successfully without the Unexpected token ) error.