message: version to 0.5.0 (next release) and build .deb for linux
diff: {
  "name": "petmate",
  - "version": "1.0.0",
  + "version": "0.5.0",
  "description": "Petmate - a C64 PETSCII graphics editor",
  "private": false,
  "author": "Janne Hellsten <jjhellst@gmail.com>",
  "linux": {
  "icon": "resources/icon.png",
  "target": [
  - "snap"
  + "deb"
  ],
  "description": "Petmate",
  "category": "Graphics"
  