Use DISPLAY=:99.0 on Linux CI

script/cibuild

@@ -62,8 +62,9 @@ def main():
 
     execute(['sh', '-e', '/etc/init.d/xvfb', 'start'])
 
-    os.environ['DISPLAY'] = ':99.0'
 
+  if PLATFORM == 'linux':
+    os.environ['DISPLAY'] = ':99.0'
 
   # CI's npm is not reliable.
   npm = 'npm.cmd' if PLATFORM == 'win32' else 'npm'

script/cibuild-linux

@@ -36,7 +36,6 @@ docker run \
   --env ELECTRON_S3_BUCKET="$BUILD_ELECTRON_ELECTRON_S3_BUCKET" \
   --env ELECTRON_S3_ACCESS_KEY="$BUILD_ELECTRON_ELECTRON_S3_ACCESS_KEY" \
   --env ELECTRON_S3_SECRET_KEY="$BUILD_ELECTRON_ELECTRON_S3_SECRET_KEY" \
-  --env DISPLAY="unix$DISPLAY" \
   --user "$UID" \
   --volume "$PWD":/workspace/electron \
   --volume /tmp/.X11-unix:/tmp/.X11-unix  \