Update travis to latest Qt

Author: jgeudens

.travis.yml

@@ -1,11 +1,12 @@
 
+os: linux
+dist: focal
+
 language: cpp
-sudo: required
-dist: bionic
 compiler: gcc
 
 before_install:
-  - sudo add-apt-repository ppa:beineri/opt-qt-5.12.6-bionic -y
+  - sudo add-apt-repository -y ppa:beineri/opt-qt-5.15.0-focal
   - sudo apt update -qq
 
 install:
@@ -14,11 +15,11 @@ install:
   - cmake -version
 
   # Dependency for Qt
-  - sudo apt -qq install mesa-common-dev libglu1-mesa-dev
+  - sudo apt install -qq mesa-common-dev libglu1-mesa-dev
 
   # Install Qt
-  - sudo apt -qq install qt512-meta-minimal qt512serialbus
-  
+  - sudo apt install -qq qt515base qt515serialbus
+
   # Setup Qt env
   - source /opt/qt*/bin/qt*-env.sh