downgrade clang version travis

.travis.yml

@@ -8,8 +8,8 @@ matrix:
       compiler: clang
       addons:
         apt:
-          sources: ['ubuntu-toolchain-r-test', 'llvm-toolchain-precise-7']
-          packages: ['clang-7', 'g++-5']
+          sources: ['ubuntu-toolchain-r-test', 'llvm-toolchain-precise-3.7']
+          packages: ['clang-3.7', 'g++-5']
 
 before_script:
   - export PATH="$PATH:$HOME/.cargo/bin"
@@ -22,6 +22,7 @@ before_install:
  - export PATH="$PATH:$HOME/.cargo/bin"
  - sudo add-apt-repository ppa:beineri/opt-qt-5.14.2-xenial -y
  - sudo apt-get update -qq
+ - sudo apt-get install libsodium-dev pkg-config
  - sudo apt-get install qt514base qt514websockets libgl1-mesa-dev
  - source /opt/qt514/bin/qt514-env.sh
  - chmod +x res/libsodium/buildlibsodium.sh