Npm test failing

[manuel-castro]

On 97c522b, npm test for me fails with following output:

> karma start ./config/karma.conf.js --single-run

/usr/people/macastro/SeungLabRepos/googleNG/neuroglancer/node_modules/karma/lib/server.js:118
  async start () {
        ^^^^^
SyntaxError: Unexpected identifier
    at Object.exports.runInThisContext (vm.js:53:16)
    at Module._compile (module.js:513:28)
    at Object.Module._extensions..js (module.js:550:10)
    at Module.load (module.js:458:32)
    at tryModuleLoad (module.js:417:12)
    at Function.Module._load (module.js:409:3)
    at Module.require (module.js:468:17)
    at require (internal/module.js:20:19)
    at Object.<anonymous> (/usr/people/macastro/SeungLabRepos/googleNG/neuroglancer/node_modules/karma/lib/cli.js:8:16)
    at Module._compile (module.js:541:32)
npm ERR! Test failed.  See above for more details.

[jbms]

I believe you need a newer version of node.js, at least >= 8. I updated package.json to include this requirement in 2d0b84c.