WebSocket connection failing due to "Upgrade" header value case sensitivity

[HusamElbashir]

I'm encountering an issue with an iOS client that fails to establish a WebSocket connection to my Hono server. The problem lies in the upgradeWebSocket function, which is unnecessarily case-sensitive to the value of the Upgrade header. Specifically, the client sends the value WebSocket as part of the handshake, and the server rejects it.

 async function upgradeWebSocket(c, next) {
  if (c.req.header('upgrade') !== 'websocket') {
    // Not websocket
    await next()
    return
  }

However per RFC 6455 Section 4.2.1 this header's value should be treated as case-insensitive:

3. An |Upgrade| header field containing the value "websocket",
   treated as an ASCII case-insensitive value.