Fix Chrome sandbox on Linux AppImage builds

.travis.yml

@@ -20,11 +20,12 @@ matrix:
             - g++-4.8
             - gcc-4.8
 
-cache:
-  directories:
-    - node_modules
-    - $HOME/.cache/electron
-    - $HOME/.cache/electron-builder
-
+before_script:
+  - | # Fix chrome-sandbox: https://github.com/electron/electron/issues/17972
+      if [[ "${TRAVIS_OS_NAME}" == "linux" ]]; then
+        echo "Fixing chrome-sandbox permissions..."
+        sudo chown root ./node_modules/electron/dist/chrome-sandbox
+        sudo chmod 4755 ./node_modules/electron/dist/chrome-sandbox
+      fi
 script:
   - npm run dist