Fix status_follow and status_unfollow assertions to accept arrays of user IDs

[DannyIsYog]

Fixes an issue reported on the forums where status_follow and status_unfollow were asserting that user_ids (and usernames) must be a string, when they should accept a table (array of strings). This caused an assertion error when users passed a list of IDs as shown in the documentation.

Updated assertions:

• status_follow: user_ids and usernames now assert table instead of string
• status_unfollow: user_ids now asserts table instead of string

Fixes: https://forum.heroiclabs.com/t/following-users-is-not-working/6516

Fixes #90

[britzl]

Thanks!