Update list of the Polkadot bootstrap nodes

[cortze]

Description

There are a bunch of outdated bootnodes in relation to the Polkadot-related networks.

This PR updates the list of nodes to use the latest version at the official repo, updating the existing nodes for:

• Polkadot Network
• Kusama Network
• Rococo Network
• Westend Network

[cortze]

Proof of not broken:

I've tested crawling the four different networks and it seems to be working fine ;) :

• Polkadot:

INFO[0173]                                              
INFO[0173] Finished crawl                                crawlDuration=2m53.214844659s crawledPeers=9013 dialablePeers=2116 undialablePeers=6897
INFO[0173] Stopped Nebula crawler.

• Kusama:

INFO[0147]                                              
INFO[0147] Finished crawl                                crawlDuration=2m27.204925586s crawledPeers=9895 dialablePeers=2338 undialablePeers=7557
INFO[0147] Stopped Nebula crawler.

• Rococo:

INFO[0089]                                              
INFO[0089] Finished crawl                                crawlDuration=1m29.894082011s crawledPeers=2433 dialablePeers=265 undialablePeers=2168
INFO[0089] Stopped Nebula crawler.

• Westend:

INFO[0063]                                              
INFO[0063] Finished crawl                                crawlDuration=1m3.661323946s crawledPeers=814 dialablePeers=118 undialablePeers=696
INFO[0063] Stopped Nebula crawler. 

[guillaumemichel]

Looks great, thanks!