updated grunt-contrib-nodeunit version to fix nodeunit exception

Grabbed the existing repo, tried running grunt - it could not load nodeunit. Here is the error message from `grunt -v nodeunit`
```
Registering "grunt-contrib-nodeunit" local Npm module tasks.
Reading /Users/gleb/git/grunt-html2js/node_modules/grunt-contrib-nodeunit/package.json...OK
Parsing /Users/gleb/git/grunt-html2js/node_modules/grunt-contrib-nodeunit/package.json...OK
Loading "nodeunit.js" tasks...ERROR
>> Error: No such module
>>     at Object.<anonymous> (/Users/gleb/git/grunt-html2js/node_modules/grunt-contrib-nodeunit/node_modules/nodeunit/lib/utils.js:14:22)
>>     at Module._compile (module.js:449:26)
```
upgrading grunt-contrib-nodeunit solved it.