Convert the package version to a string before sending it

This is what Jupyter expects.

Author: JamesWrigley

src/handlers.jl

@@ -170,7 +170,7 @@ function kernel_info_request(socket, kernel, msg)
                  msg_reply(msg, "kernel_info_reply",
                            Dict("protocol_version" => "5.4",
                                         "implementation" => "ijulia",
-                                        "implementation_version" => pkgversion(@__MODULE__),
+                                        "implementation_version" => string(pkgversion(@__MODULE__)),
                                         "language_info" =>
                                         Dict("name" => "julia",
                                              "version" =>