regression: sort out duplicated gems

```
WARN: Unresolved or ambiguous specs during Gem::Specification.reset:
      fiddle (>= 0)
      Available/installed versions of this gem:
      - 1.1.8
      - 1.1.1
      tsort (< 0.3)
      Available/installed versions of this gem:
      - 0.2.0
      - 0.1.1
WARN: Clearing out unresolved specs. Try 'gem cleanup <gem>'
Please report a bug if this causes problems.
```