add Checksums-Sha512 to isMultilineField
add Checksums-Sha512 to isMultilineField

Otherwise line breaks are not properly handled and the output contains
excess newlines

Fixes #361

smira/aptly,adfinis-forks/aptly,smira/aptly,adfinis-forks/aptly,aptly-dev/aptly,jola5/aptly,sobczyk/aptly,smira/aptly,jola5/aptly,aptly-dev/aptly,jola5/aptly,sobczyk/aptly,sobczyk/aptly,neolynx/aptly,adfinis-forks/aptly,aptly-dev/aptly,neolynx/aptly,neolynx/aptly