.travis.yml in stellar-base-0.17.0 vs .travis.yml in stellar-base-0.18.0

- old
+ new

@@ -2,9 +2,13 @@
 rvm:
 - 2.2.6
 - 2.3.3
 - 2.4.0
 - 2.5.1
+before_install:
+  - sudo add-apt-repository -y ppa:chris-lea/libsodium
+  - sudo apt-get -y update
+  - sudo apt-get install -y libsodium-dev
 script: bundle exec rake travis
 notifications:
   slack:
     secure: V/6a8KFe067uukrbCJA2R1HPO4xy0YSQ1pwmHVRi5StX+yl+lYsWWJdjdBdT0j3iJBYyPRqU4bQYck+OloxtELnrHCX+OkodxcxW8W/ACc914iIf0FyY9pnusK7ck2awmt4Iuf94YPgi0XTm1aCcm+f0yU7wiIVFpftoXSk1EDY=