api-server: add jshint to devDependencies

`package.json` scaffolded by api-server template includes a `pretest` script executing `jshint`, but `jshint` is not included as a dependency.

This causes `npm test` in the scaffolded project to fail on machines where jshint is not installed globally.

This change fixes the problem by adding `jshint` to `devDependencies`.

The test are failing on a machine without a global jshint due to a bug in strong-cached-install - see https://github.com/strongloop/strong-cached-install/pull/4. However, since they are failing without this patch too, IMO we don't have to wait for that other PR to be landed first.

/to @ritch please review