add immutable to cache control header

Author: BryanCrotaz

README.md

@@ -192,7 +192,7 @@ The client specified MUST implement functions called `getObject` and `putObject`
 
 Sets the `Cache-Control` header on the uploaded files.
 
-*Default:* `max-age=63072000, public`
+*Default:* `max-age=63072000, public, immutable`
 
 ### expires
 

index.js

@@ -21,7 +21,7 @@ module.exports = {
         prefix: '',
         profile: '',
         acl: 'public-read',
-        cacheControl: 'max-age='+TWO_YEAR_CACHE_PERIOD_IN_SEC+', public',
+        cacheControl: 'max-age='+TWO_YEAR_CACHE_PERIOD_IN_SEC+', public, immutable',
         expires: EXPIRE_IN_2030,
         dotFolders: false,
         batchSize: 0,

tests/index-test.js

@@ -197,7 +197,7 @@ describe('s3 plugin', function() {
 
       assert.equal(context.config.s3.filePattern, '**/*.{js,css,png,gif,ico,jpg,webp,map,xml,txt,svg,swf,eot,ttf,woff,woff2,otf,wasm,json}');
       assert.equal(context.config.s3.prefix, '');
-      assert.equal(context.config.s3.cacheControl, 'max-age=63072000, public');
+      assert.equal(context.config.s3.cacheControl, 'max-age=63072000, public, immutable');
       assert.equal(new Date(context.config.s3.expires).getTime(), new Date('Tue, 01 Jan 2030 00:00:00 GMT').getTime());
     });
   });