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`.
Merge pull request #157 from strongloop/fix/add-jshint-to-template

api-server: add jshint to devDependencies