comment about #676 fix

I reviewed the fix for #676 and have a comment about it. Unfortunately #676 cannot be reopened, so that is why the new ticket was open.

Why are `timestamp` and `sequence_number` still converted via `float64` ?
https://github.com/influxdb/influxdb/commit/dcc1c9a2e02c9a2a34a243b1a3439813f52bf24e#diff-5f4e7a2764de0f93aa09e2d68927b6aaR71
https://github.com/influxdb/influxdb/commit/dcc1c9a2e02c9a2a34a243b1a3439813f52bf24e#diff-5f4e7a2764de0f93aa09e2d68927b6aaR94
It seems at least superfluous and can cause the same bug (for example with user-generated `sequence_number`)
The json spec doesn't have a distinction but if it's not supposed to be a float we can enforce it like we do with other requirements on the data (e.g. "Cannot have duplicate field names" or "invalid payload" errors).

Not a huge deal but seems to me it would be better to enforce what we expect the data to look like since we're having to do the parsing anyway.  Less code for us and forces data to be consistent.