don't make AppImages

Ubuntu won't run AppImages because of sandboxing: see
electron/electron#42510

Author: christianp

package.json

@@ -22,7 +22,7 @@
     "dist": "electron-builder",
     "build_windows": "electron-builder --win portable msi",
     "build_mac": "electron-builder --macos --universal",
-    "build_linux": "electron-builder --linux AppImage deb"
+    "build_linux": "electron-builder --linux deb"
   },
   "build": {
     "files": [