Missing migration for org.scalatest.concurrent.Timeouts

[olafurpg]

First of all, thank you for providing this migration rewrite! I have already upgraded several projects to 3.1.0 and it's been mostly a seamless experience so far thanks to the rewrite and automatic Scala Steward PRs.

When upgrading the Scalafmt repo we hit on the following compile error after applying the rewrite scalameta/scalafmt#1582

[error] /home/travis/build/scalameta/scalafmt/scalafmt-tests/src/test/scala/org/scalafmt/FormatTests.scala:24:8: object Timeouts is not a member of package org.scalatest.concurrent

[error] import org.scalatest.concurrent.Timeouts

[error]        ^

[error] /home/travis/build/scalameta/scalafmt/scalafmt-tests/src/test/scala/org/scalafmt/FormatTests.scala:32:10: not found: type Timeouts

[error]     with Timeouts

[error]          ^

From the release notes

Removed the deprecated org.scalatest.concurrent.Timeouts trait. Please use org.scalatest.concurrent.TimeLimits instead.

http://www.scalatest.org/release_notes/3.1.0