Current master (bb95272) is unable to parse the json given by the API

[Louis]

Affected functions (the list is not exhaustive):

• im_history
• channels_history
• groups_history
• users_list
• files_list

How to reproduce in utop:

# let channel = Slacko.channel_of_string "#random";;
val channel : Slacko.channel = <abstr>
# Slacko.channels_history token channel;;
- : Slacko.history_result = `ParseFailure "Slacko.history_obj.latest"