Add rpm building

.travis.yml

@@ -21,6 +21,7 @@ addons:
       - icnsutils
       - graphicsmagick
       - xz-utils
+      - rpm
 
 # Handle git submodules yourself 
 git:

electron-builder.json

@@ -38,7 +38,8 @@
     "maintainer": "JGraph <support@draw.io>",
     "target": [
       "AppImage",
-      "deb"
+      "deb",
+      "rpm"
     ]
   }
 }