Make husky hooks silent

I get bunch of npm output, if precommit/prepush hook is failing:

```
npm ERR! bar.export@0.0.0 precommit: `gulp lint`
npm ERR! Exit status 1
npm ERR!
npm ERR! Failed at the bar.export@0.0.0 precommit script.
npm ERR! This is most likely a problem with the bar.export package,
npm ERR! not with npm itself.
npm ERR! Tell the author that this fails on your system:
npm ERR!     gulp lint
npm ERR! You can get their info via:
npm ERR!     npm owner ls bar.export
npm ERR! There is likely additional logging output above.
npm ERR! System Darwin 13.2.0
npm ERR! command "node" "/usr/local/bin/npm" "run" "precommit"
npm ERR! cwd /Users/floatdrop/bar.export
npm ERR! node -v v0.10.28
npm ERR! npm -v 1.4.16
npm ERR! code ELIFECYCLE
npm ERR!
npm ERR! Additional logging details can be found in:
npm ERR!     /Users/floatdrop/bar.export/npm-debug.log
npm ERR! not ok code 0
```

This is kind of distracting - you should scroll up to see actual errors. So may be append `--silent` to npm run command?