fix: gracefully handle SIGPIPE

[branchvincent]

When fixing #234, I noticed cleo's terminal prompt wasn't rendering until after reading a response:

$ poetry cache clear --all .
no # cleo is prompting here
Delete 575 entries? (yes/no) [no] # but output is displayed later

This was introduced via #165, since now we aren't always flushing the output. This reverts that and instead suppresses a broken pipe error, which was the initial motivation for that PR.
Note that click also always flushes output and similary ignores broken pipes.

I manually tested this with poetry -V | head -1

Closes #56

[Secrus]

I think this could resolve #56, could you confirm?