portable-screencap: remove set options
portable-screencap: remove set options

- `set -o pipefail` is not portable as dash doesn't know about it, and

- `set -e` is not very useful if you have a die() function, and
  [has some problems too](http://mywiki.wooledge.org/BashFAQ/105).

jbenet/ipfs-screencap,lgierth/ipfs-screencap