Update rails version to 4.2.0
Use web-console instead of better_errors
Suppress deprecation warning: ActionMailer::Base#deliver

```
DEPRECATION WARNING: #deliver is deprecated and will be removed in Rails
5. Use #deliver_now to deliver immediately or #deliver_later to deliver
through Active Job.
```
Rewrite `serve_static_assets` option with `serve_static_files`

Rails 4.2 has API change and shows the following warning:
```
DEPRECATION WARNING: The configuration option
`config.serve_static_assets` has been renamed to
`config.serve_static_files` to clarify its role (it merely enables
serving everything in the `public` folder and is unrelated to the asset
pipeline). The `serve_static_assets` alias will be removed in Rails 5.0.
Please migrate your configuration files accordingly.
```
Renamed *.css.scss files to *.scss
rake rails:update
Merge pull request #38 from tricknotes/rails-42

Update Rails version to 4.2.0