package.json: Don't check src/ with eslint
package.json: Don't check src/ with eslint

There are no .js/.jsx files in /src:
```
$ find src/ -name "*.js"
$ find src/ -name "*.jsx"
```

Then running `eslint:fix` fails:
```
$ npm run eslint:fix:fix

Oops! Something went wrong! :(

No files matching the pattern "src/" were found.
Please check for typing mistakes in the pattern.

npm ERR! code ELIFECYCLE
npm ERR! errno 2
npm ERR! CockpitDevelopmentDependencies@ eslint:fix: `eslint --fix --ext .js --ext .jsx pkg/ src/`
```

garrett/cockpit,martinpitt/cockpit,martinpitt/cockpit,cockpit-project/cockpit,garrett/cockpit,martinpitt/cockpit,mvollmer/cockpit,martinpitt/cockpit,garrett/cockpit,mvollmer/cockpit,garrett/cockpit,martinpitt/cockpit,cockpit-project/cockpit,cockpit-project/cockpit,mvollmer/cockpit,mvollmer/cockpit,cockpit-project/cockpit,mvollmer/cockpit,cockpit-project/cockpit,garrett/cockpit