Change timing of take a screenshot.

## Motivation

Take screenshot too.

- Hypertrophy of the report file size
- Decrease in execution speed

It should kept to minimum necessary take screenshots.

## Solution

### Current

Before process of Capybara::Session::NODE_METHODS

- [lib/gnawrnip/ext/capybara/session.rb](https://github.com/gongo/gnawrnip/blob/cfb6d3db348a6f3e75f40bcacf93acb176861aba/lib/gnawrnip/ext/capybara/session.rb#L13-L14)
- https://github.com/jnicklas/capybara/blob/2.4.1/lib/capybara/session.rb#L27-L38

### New timing 1

Only verification process **immediately after** the action process.

- verification process
    - `has_text?`, `has_select?`, etc..
- action process
    - `click`, `fill_in`, etc...

### New timing 2

Taking every **step**