Fixes indentation for use with `david` tool from `david-dm`.

`grunt-cli-mocha` is using [david-dm](https://david-dm.org/Rowno/grunt-mocha-cli) to track dependency updates. There exists an npm package [david](https://npmjs.org/package/david) that checks project dependencies for updates via the command `david update` and writes to `package.json`.

Previous to this commit, use of this tool would generate a meaningless diff due to the nonstandard `package.json` indentation in the `grunt-cli-mocha` project.

This commit regenerates `package.json` with david-compatible indentation for friendlier diffs.