Fix almond `module path does not exist` issue

The build was failing due to a change in `grunt-requirejs` I think. This was the error: 

```
>> Error: Error: ERROR: module path does not exist: /Users/Piet/Projects/net/node_modules/grunt-requirejs/node_modules/almond/almond.js.js for module named: almond. Path is relative to: /Users/Piet/Projects/net.js
>>     at /Users/Piet/Projects/net.js/node_modules/grunt-requirejs/node_modules/requirejs/bin/r.js:26058:35
```

Switched grunt-requirejs for grunt-contrib-requirejs and added almond as a dependency.

All tests were green. :)