fix: remove support for outdated browsers

BREAKING CHANGE: browser versions before Chrome 76, Firefox 68 and Opera 63
are no longer supported

package.json

@@ -32,10 +32,10 @@
     "release": "standard-version"
   },
   "browserslist": [
-    "Chrome >= 55",
-    "Firefox >= 53",
-    "FirefoxAndroid >= 57",
-    "Opera >= 42"
+    "Chrome >= 76",
+    "Firefox >= 68",
+    "FirefoxAndroid >= 68",
+    "Opera >= 63"
   ],
   "dependencies": {
     "@material/theme": "^4.0.0",

src/manifest.json

@@ -10,11 +10,11 @@
   "browser_specific_settings": {
     "gecko": {
       "id": "{e58d3966-3d76-4cd9-8552-1582fbc800c1}",
-      "strict_min_version": "53.0"
+      "strict_min_version": "68.0"
     }
   },
-  "minimum_chrome_version": "55.0",
-  "minimum_opera_version": "42.0",
+  "minimum_chrome_version": "76.0",
+  "minimum_opera_version": "63.0",
 
   "permissions": [
     "storage",