Errors on building (needs update on README.md)

[salkz]

Might be helpful to try building your stuff on a fresh virtual machine or something. I didn't have grunt before so after:

henry@dev:~/test/pie-chart$ sudo npm install -g grunt-cli
henry@dev:~/test/pie-chart$ grunt

I was greeted by:

Loading "grunt-karma.js" tasks...ERROR
>> Error: Cannot find module 'karma'
Warning: Task "karma:continuous" not found. Use --force to continue.

And after

henry@dev:~/test/pie-chart$ npm install karma --save-dev
henry@dev:~/test/pie-chart$ npm install grunt-karma --save-dev
henry@dev:~/test/pie-chart$ grunt

I got this output:

Running "jshint:gruntfile" (jshint) task
>> 1 file lint free.

Running "jshint:test" (jshint) task
>> 1 file lint free.

Running "concat:utils" (concat) task
File "/tmp/utils.js" created.

Running "concat:js" (concat) task
File "dist/pie-chart.js" created.

Running "concat:test" (concat) task
File "dist/pie-chart.spec.js" created.

Running "uglify:js" (uglify) task
File "dist/pie-chart.min.js" created.

Running "karma:continuous" (karma) task
WARN `start` method is deprecated since 0.13. It will be removed in 0.14. Please use
  server = new Server(config, [done])
  server.start()
instead.
Warning: Invalid configuration: client.args must be an array of strings Use --force to continue.

Aborted due to warnings.