Upgrade haml_lint Gem to 0.26.0

What does this MR do?

Upgrade the haml_lint Gem to use the latest version (0.26.0).

Why was this MR needed?

To have support for disabling linters with comments. (https://github.com/brigade/haml-lint/commit/0e3a25cfc42e79b4b6d3d6ab7af2367fe1fa2ba1#diff-04c6e90faac2675aa89e2176d2eec7d8R147)

What are the relevant issue numbers?

#34903 (closed)

https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/9742#note_28099787