Fixed invalid grunt-commonjs version in package.json

Running `npm install` with grunt-commonjs version `0.2.0rc7` fails with subsequent output. Fixed to valid `0.2.0-rc7`.

```
npm http GET https://registry.npmjs.org/grunt-commonjs
npm http 304 https://registry.npmjs.org/grunt-commonjs
npm ERR! Error: No compatible version found: grunt-commonjs@'>=0.2.0rc7 <0.3.0-'
npm ERR! Valid install targets:
npm ERR! ["0.1.0","0.1.0-rc7","0.2.0-rc7"]
npm ERR!     at installTargetsError (/usr/local/lib/node_modules/npm/lib/cache.js:682:10)
npm ERR!     at next (/usr/local/lib/node_modules/npm/lib/cache.js:661:17)
npm ERR!     at /usr/local/lib/node_modules/npm/lib/cache.js:641:5
npm ERR!     at saved (/usr/local/lib/node_modules/npm/node_modules/npm-registry-client/lib/get.js:138:7)
npm ERR!     at Object.oncomplete (fs.js:297:15)
npm ERR! If you need help, you may report this log at:
npm ERR!     <http://github.com/isaacs/npm/issues>
npm ERR! or email it to:
npm ERR!     <npm-@googlegroups.com>

npm ERR! System Darwin 12.5.0
npm ERR! command "node" "/usr/local/bin/npm" "install"
npm ERR! cwd /Users/vlki/Projects/GoodData/interactive-goodsupport
npm ERR! node -v v0.8.22
npm ERR! npm -v 1.2.14
npm ERR! 
npm ERR! Additional logging details can be found in:
npm ERR!     /Users/vlki/Projects/GoodData/interactive-goodsupport/npm-debug.log
npm ERR! not ok code 0
```