Updater: fix update.sh parsing of latest version

[onetechnical]

Summary

With the removal of S3 credential requirements, the updater script has an additional output line to indicate it's using anonymous credentials. This breaks the parsing of version. This changes the sed from counting lines to just taking the last line with tail.

Test Plan

Verify that nightly integration works properly.

[onetechnical]

This might have broken nightly updaters, as they can't run their update.sh!

[codecov]

Codecov Report

Merging #4994 (bb48b66) into master (ecdcbf9) will decrease coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #4994      +/-   ##
==========================================
- Coverage   53.63%   53.61%   -0.03%     
==========================================
  Files         432      432              
  Lines       54057    54057              
==========================================
- Hits        28996    28981      -15     
- Misses      22818    22826       +8     
- Partials     2243     2250       +7     

Impacted Files	Coverage Δ
crypto/merkletrie/trie.go	66.42% <0.00%> (-2.19%)	⬇️
agreement/cryptoVerifier.go	67.60% <0.00%> (-2.12%)	⬇️
agreement/proposalManager.go	96.07% <0.00%> (-1.97%)	⬇️
crypto/merkletrie/node.go	91.62% <0.00%> (-1.87%)	⬇️
catchup/peerSelector.go	98.95% <0.00%> (-1.05%)	⬇️
cmd/tealdbg/debugger.go	72.69% <0.00%> (-0.81%)	⬇️
ledger/testing/randomAccounts.go	56.26% <0.00%> (-0.62%)	⬇️
data/transactions/verify/txn.go	70.24% <0.00%> (-0.49%)	⬇️
catchup/service.go	69.32% <0.00%> (ø)
network/wsNetwork.go	64.92% <0.00%> (+0.17%)	⬆️
... and 1 more

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