Remove use of @asserts in some areas?

[DilumAluthge]

I've noticed some uses of @assert, e.g.

JWTs.jl/src/JWTs.jl

Lines 114 to 117 in 8eeb318

	function kid(jwt::JWT)::String
	@assert issigned(jwt)
	get(decodepart(jwt.header), "kid", nothing)
	end

In a future minor version of Julia, @asserts may be disabled by default.

Therefore, I think that most (if not all) uses of @assert in this package should be removed and replaced with regular errors, e.g.

function kid(jwt::JWT)::String 
     issigned(jwt) || throw(ArgumentError("jwt is not signed"))
     get(decodepart(jwt.header), "kid", nothing) 
 end