Don't modify multiline strings between seed and database

Got a problem with multiline string export from database.
When a field contains a string with multiple lines, some tab character where added to the string in seed files. This can lead to problems later (in my case, parsing this as a markdown string because markdown expect 1 tab as a quote block).
It's better to leave the string exactly as it is in the database (in order to get the exact same state when transfering database to seed files and back)

This pull request fix this issue by formating array in a pretty format (same format as before) but ignores multilines strings (leave them as is).