Drop unneeded dependencies on Travis

.travis.yml

@@ -6,19 +6,17 @@ matrix:
       node_js: '12'
 
     - os: linux
+      dist: bionic
+      sudo: true
       language: node_js
       node_js: '12'
       addons:
         apt:
-          sources:
-            - ubuntu-toolchain-r-test
           packages:
             - libx11-dev
             - zlib1g-dev
-            - libpng12-dev
+            - libpng-dev
             - libxtst-dev
-            - g++-4.8
-            - gcc-4.8
 
 before_script:
   - | # Fix chrome-sandbox: https://github.com/electron/electron/issues/17972