Wrong error message when attaching child epic

A: https://staging.gitlab.com/groups/gitlab-org/-/epics/22
Alpha: https://staging.gitlab.com/groups/gitlab-org/-/epics/29
In the below diagram, A is the parent of B, etc.

graph TD;
  A-->B;
  B-->C;
  C-->D;
  D-->E;

  Alpha-->Beta

When I attempt to add A as a child of Beta, I get an error message. But it's not the correct error message since it talks about "an issue". We can just use the same error message of having too deep epic hierarchies. See below:

Edited Jan 07, 2019 by Victor Wu