Fix unnecessary horizontal scroll area in pipeline visualizations

## What does this MR do?

Removes a min-width attribute for the build pipeline visualization wrapper

## Are there points in the code the reviewer needs to double check?

I am curious why this line was there in the first place.  Perhaps I'm just not seeing it.

## Why was this MR needed?

I was noticing an unnecessary horizontal scroll bar when viewing pipeline visualizations embedded in merge request builds tab:
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/5627/builds

## What are the relevant issue numbers?

Line appears to have been introduced in !5742

## Screenshots (if relevant)

![Screen_Shot_2016-08-24_at_11.15.13_PM](/uploads/e395ed8d4415187735d06b8386fe4633/Screen_Shot_2016-08-24_at_11.15.13_PM.png)

## Does this MR meet the acceptance criteria?

As this is a very simple cosmetic change, I don't think it warrants inclusion in the changelog, documentation, or tests.

- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !6005