Handle the exceptions better in cli.py

[tlkamp]

No description provided.

[codecov-io]

Codecov Report

Merging #36 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master      #36   +/-   ##
=======================================
  Coverage   96.47%   96.47%           
=======================================
  Files           7        7           
  Lines         142      142           
=======================================
  Hits          137      137           
  Misses          5        5

Impacted Files	Coverage Δ
ouroboros/cli.py	100% <100%> (ø)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update aa3bc22...50e8727. Read the comment docs.