Rich text editor edit bar is overflowing its container

Summary

The content of the edit bar in the Rich text editor is overflowing its container on small screens.

Steps to reproduce

1. In any project, go to "Wiki" and create a new page or edit an existing one.
2. Above the Content editor, select "Edit rich text"
3. Resize your window to less than 1000px wide
4. Notice the edit bar content overflow to the left

What is the current bug behavior?

The content overflows its container to the left

What is the expected correct behavior?

The content should either wrap or hide less used buttons in a dropdown

Relevant logs and/or screenshots

Output of checks

This bug happens on GitLab.com

Results of GitLab environment info

Expand for output related to GitLab environment info

(For installations with omnibus-gitlab package run and paste the output of:
`sudo gitlab-rake gitlab:env:info`)

(For installations from source run and paste the output of:
`sudo -u git -H bundle exec rake gitlab:env:info RAILS_ENV=production`)

Results of GitLab application Check

Expand for output related to the GitLab application check

(For installations with omnibus-gitlab package run and paste the output of:
sudo gitlab-rake gitlab:check SANITIZE=true)
(For installations from source run and paste the output of:
sudo -u git -H bundle exec rake gitlab:check RAILS_ENV=production SANITIZE=true)
(we will only investigate if the tests are passing)

Possible fixes