feat(icon): default purpose to any + maskable

Author: pi0

docs/content/en/icon.md

@@ -48,13 +48,13 @@ Will return an empty string when no icon in the given size is available (eg. whe
 Name of property for accessible icons.
 
 **purpose**
-- Default: null
+- Default: `['any', 'maskable']`
 
 Array or string of icon purpose.
+
 Example:
+
 ```js
-purpose: [ 'badge', 'maskable' ]
-// or
 purpose: 'maskable'
 ```
 

lib/icon/module.js

@@ -37,7 +37,7 @@ async function run (pwa, _emitAssets) {
     iconProperty: '$icon',
     publicPath,
     iconSrc: null,
-    purpose: null,
+    purpose: ['any', 'maskable'],
 
     _iconHash: null,
     _cacheDir: null,