Elixir 1.15.2, otp 25.0 - bitstring specifier does not exist warnings

[pradeep-in]

Getting a lot of these warnings, but seem like they could be an issue at some point. Or is it fine?

warning: bitstring specifier "int64" does not exist and is being expanded to "int64()", please use parentheses to remove the ambiguity
  lib/bson/encoder.ex:54: BSON.Encoder.encode/1

[zookzook]

I guess it is fine because these bitstring specifiers are macros. I will add the missing parentheses.

[zookzook]

The PR #195 fixes the warnings.