Fix typo related to pico-bitcoin conversion

[t-bast]

Fixes #1502

[codecov-commenter]

Codecov Report

Merging #1503 into master will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1503   +/-   ##
=======================================
  Coverage   86.73%   86.73%           
=======================================
  Files         137      137           
  Lines       10738    10738           
  Branches      461      461           
=======================================
  Hits         9314     9314           
  Misses       1424     1424           

Impacted Files	Coverage Δ
...scala/fr/acinq/eclair/payment/PaymentRequest.scala	92.09% <100.00%> (ø)
...c/main/scala/fr/acinq/eclair/channel/Channel.scala	86.04% <0.00%> (-0.45%)	⬇️
...nq/eclair/blockchain/electrum/ElectrumClient.scala	73.80% <0.00%> (-0.37%)	⬇️
.../eclair/payment/relay/PostRestartHtlcCleaner.scala	87.33% <0.00%> (+1.33%)	⬆️
...main/scala/fr/acinq/eclair/router/Validation.scala	92.91% <0.00%> (+1.49%)	⬆️