Shellcheck: readarray/mapfile should create variables

[rmmh]

Bash readarray/mapfile assign variables, but shellcheck doesn't understand.

#!/bin/bash
readarray blah <<< $'hi\nthere'
echo "${blah[@]}"

In foo.sh line 3:
echo "${blah[@]}"
      ^-- SC2154: blah is referenced but not assigned.

[koalaman]

Fixed in 509cda4