docs: correct typo in private key type #3904

Job	Run time
Build	2m 57s
Test example js-libp2p-example-browser-pubsub	2m 17s
Test example js-libp2p-example-chat	59s
Test example js-libp2p-example-circuit-relay	1m 34s
Test example js-libp2p-example-connection-encryption	58s
Test example js-libp2p-example-custom-protocols	55s
Test example js-libp2p-example-delegated-routing	1m 45s
Test example js-libp2p-example-discovery-mechanisms	1m 16s
Test example js-libp2p-example-peer-and-content-routing	1m 10s
Test example js-libp2p-example-pnet	1m 26s
Test example js-libp2p-example-protocol-and-stream-muxing	1m 29s
Test example js-libp2p-example-pubsub	1m 3s
Test example js-libp2p-example-transports	1m 5s
Test example js-libp2p-example-webrtc-private-to-private	2m 21s
	21m 15s

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