chore: use standard manifest key

gulpfile.js

@@ -141,7 +141,7 @@ gulp.task('manifest', function(done) {
         fileName: 'manifest.json',
         edit: (parsedJson, file) => {
           if (['chrome', 'edge', 'opera'].includes(targetEnv)) {
-            delete parsedJson.applications;
+            delete parsedJson.browser_specific_settings;
             delete parsedJson.options_ui.browser_style;
           }
 

src/manifest.json

@@ -7,7 +7,7 @@
   "homepage_url": "https://github.com/dessant/buster",
   "default_locale": "en",
 
-  "applications": {
+  "browser_specific_settings": {
     "gecko": {
       "id": "{e58d3966-3d76-4cd9-8552-1582fbc800c1}",
       "strict_min_version": "53.0"