Fix onerror handler

[eyr1n]

Changelog

EventEmitter always emits values of Error types on "error", not undefined.

Description

According to the documentation of ws module for Node.js, onerror handler emits Error types.
However, WebSocket in the browser does not emits event.error. This behavior is incorrect as per the code below.

ws-protocol/typescript/ws-protocol/src/FoxgloveClient.ts

Line 29 in 736c8df

error: (error: Error) => void;

I fixed to always emits values of Error types on "error".

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[achim-k]

I think this is fine. AFAIU, in the browser the error event does not contain any information so just emitting a new Error seems OK