Change libsodium version on ubuntu

ci/travis/before_install.sh

@@ -32,7 +32,7 @@ then
     chmod +x qt-opensource-linux-x64-5.8.0.run
     ./qt-opensource-linux-x64-5.8.0.run --script $HOME/build/duniter/sakia/ci/travis/qt-installer-noninteractive.qs
 
-    wget http://archive.ubuntu.com/ubuntu/pool/universe/libs/libsodium/libsodium13_1.0.1-1_amd64.deb
+    wget http://archive.ubuntu.com/ubuntu/pool/universe/libs/libsodium/libsodium18_1.0.11-2_amd64.deb
     sudo dpkg -i libsodium13_1.0.1-1_amd64.deb
     rm -r ~/.pyenv
     git clone https://github.com/yyuu/pyenv.git ~/.pyenv