Set version to v0.3.1

[sstone]

No description provided.

[codecov-io]

Codecov Report

Merging #1061 into master will increase coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1061      +/-   ##
==========================================
+ Coverage   82.43%   82.45%   +0.01%     
==========================================
  Files          99       99              
  Lines        7551     7551              
  Branches      293      293              
==========================================
+ Hits         6225     6226       +1     
+ Misses       1326     1325       -1

Impacted Files	Coverage Δ
...clair/blockchain/electrum/ElectrumClientPool.scala	74.19% <0%> (-4.31%)	⬇️
...c/main/scala/fr/acinq/eclair/channel/Channel.scala	83.88% <0%> (-0.1%)	⬇️
...-core/src/main/scala/fr/acinq/eclair/io/Peer.scala	75.23% <0%> (+0.3%)	⬆️
...nq/eclair/blockchain/electrum/ElectrumClient.scala	74.34% <0%> (+0.37%)	⬆️
...src/main/scala/fr/acinq/eclair/router/Router.scala	86.76% <0%> (+0.94%)	⬆️