We provide only pkcs8 keys, if you cannot use pkcs8 you can use the pkcs1 encoding, use openssl to convert
The following command was tested on the version 2.6.5
$ openssl version
LibreSSL 2.6.5
When prompet to enter password, don't enter a password, just press the enter or return key on you keyboard
$ openssl pkcs8 -in pkcs1_pk.pem -out pkcs1_pk.pem