removes bashism

2 jobs for develop in 1 minute and 38 seconds (queued for 3 seconds)
Name Stage Failure
failed
deploy-develop Deploy There is an unknown failure, please try again
fetch http://dl-cdn.alpinelinux.org/alpine/v3.5/main/x86_64/APKINDEX.tar.gz
fetch http://dl-cdn.alpinelinux.org/alpine/v3.5/community/x86_64/APKINDEX.tar.gz
(1/1) Installing openssh-client (7.4_p1-r0)
Executing busybox-1.25.1-r0.trigger
OK: 20 MiB in 24 packages
$ eval $(ssh-agent -s)
Agent pid 20
$ echo $SSH_PRIVATE_KEY | ssh-add -
Enter passphrase for (stdin):
ERROR: Job failed: exit code 1