`skiping` => `skipping`
Fixed typos in shallow routes and routing concerns

Grammatical tense correction: "There exists two" => "There exist two".
Plurality correction: "can be reused inside others resources" => "can be reused inside other resources".
Merge pull request #12942 from kuldeepaggarwal/typos

`skiping` => `skipping` [ci skip]
Merge pull request #12945 from fluxusfrequency/patch-1

Fixed typos in "shallow routes" and "routing concerns" in routing.md [ci skip]
[ci skip] `apropriate` => `appropriate`, spaces added
Merge pull request #12949 from akshay-vishnoi/documentation

[ci skip] `apropriate` => `appropriate`, spaces added
use `4-0-stable` arel branch to get bundle working again.

this resolves the following error when running `bundle install`

```
ArgumentError: wrong number of arguments (2 for 1)
    /Users/senny/Projects/rails/.bundle/bundler/gems/arel-454a25f18c95/lib/arel/crud.rb:5:in `compile_update'
```

The build is still broken with lots of:

```
ArgumentError: wrong number of arguments (2 for 1)
    /Users/senny/Projects/rails/.bundle/bundler/gems/arel-454a25f18c95/lib/arel/crud.rb:5:in `compile_update'
```
use arel `master` and update activerecord to depend on arel `5.0.0`.

This is a follow-up to 3053fee954c1e28b23f7e00921d7b9b3b3867fa5.

> The `master` branch should use the `master` branch.