Move ejs dependency from devDependencies to dependencies

Hi there,

In your task https://github.com/werk85/grunt-ng-constant/blob/master/tasks/ngconstant.js#L14  you have a dependency to `ejs` but you put it in `devDependencies`.

People that use your task and only have `grunt-ng-constant` in the `devDependencies` of their `package.json` won't be able to retrieve transitive dependency to `ejs`.