Describe the bug
After the 1.5.0 release, there appears to have been a significant reduction in performance. For instance, here is the output of time bandit -r . using 1.4.0:

17.56user 2.12system 0:21.22elapsed 92%CPU (0avgtext+0avgdata 90712maxresident)k
182728inputs+0outputs (0major+45973minor)pagefaults 0swaps

And here it is with 1.5.0:

261.46user 3.96system 4:27.26elapsed 99%CPU (0avgtext+0avgdata 89164maxresident)k
362728inputs+0outputs (8major+45690minor)pagefaults 0swaps

To Reproduce
Steps to reproduce the behavior:

1. Run time bandit -r . within a medium to large-size project on 1.4.0
2. Note the time.
3. Run the same command again, but with bandit 1.5.0
4. Compare the two times. You should see a significant drop in performance

Expected behavior
Performance consistent or comparable with 1.4.0

Bandit version

bandit 1.5.0
  python version = 2.7.15rc1 (default, Apr 15 2018, 21:51:34) [GCC 7.3.0]