Update grunt-exec to version 0.4.7 🚀

[greenkeeperio-bot]

Hello 👋

🚀🚀🚀

grunt-exec just published its new version 0.4.7, which is not covered by your current version range.

If this pull request passes your tests you can publish your software with the latest version of grunt-exec – otherwise use this branch to work on adaptions and fixes.

Happy fixing and merging 🌴

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The new version differs by 6 commits .

• 1bec091 Release of grunt version fix
• d4dc55c 0.4.7-0
• dabdad6 Change grunt requirement to allow newer versions
• 395ec80 jshint fixes, basic Windows support for grunt tasks
• 0413875 Minor readme changes, etc
• e3d60a2 Drop ci for node 0.8.

See the full diff.

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