Add RuboCop Capybara

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (4cfe3a2) 92.39% compared to head (615ce6a) 92.39%. Report is 3 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #548 +/- ## ======================================= Coverage 92.39% 92.39% ======================================= Files 17 17 Lines 460 460 ======================================= Hits 425 425 Misses 35 35 ``` | [Files](https://app.codecov.io/gh/activeadmin/arbre/pull/548?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=activeadmin) | Coverage Δ | | |---|---|---| | [lib/arbre/context.rb](https://app.codecov.io/gh/activeadmin/arbre/pull/548?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=activeadmin#diff-bGliL2FyYnJlL2NvbnRleHQucmI=) | `100.00% <100.00%> (ø)` | | | [lib/arbre/element/builder\_methods.rb](https://app.codecov.io/gh/activeadmin/arbre/pull/548?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=activeadmin#diff-bGliL2FyYnJlL2VsZW1lbnQvYnVpbGRlcl9tZXRob2RzLnJi) | `100.00% <100.00%> (ø)` | | | [lib/arbre/html/tag.rb](https://app.codecov.io/gh/activeadmin/arbre/pull/548?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=activeadmin#diff-bGliL2FyYnJlL2h0bWwvdGFnLnJi) | `93.68% <100.00%> (ø)` | |

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[javierjulio]

@tagliala this looks great and seems ready. Was it ready for review? Let me know.

[tagliala]

Yes, it was ready