Get date and format for UTC (matches jupyter server)

Author: halleysfifthinc

src/IJulia.jl

@@ -36,7 +36,7 @@ export notebook, jupyterlab, installkernel
 using ZMQ, JSON, SoftGlobalScope
 import Base.invokelatest
 import Dates
-using Dates: now
+using Dates: now, format, @dateformat_str, UTC, ISODateTimeFormat
 import Random
 using Base64: Base64EncodePipe
 import REPL

src/msg.jl

@@ -18,7 +18,7 @@ end
 msg_header(m::Msg, msg_type::String) = Dict("msg_id" => uuid4(),
                                             "username" => m.header["username"],
                                             "session" => m.header["session"],
-                                            "date" => now(),
+                                            "date" => format(now(UTC), ISODateTimeFormat)*"Z",
                                             "msg_type" => msg_type,
                                             "version" => "5.4")