Options: use MD icons in the language editor buttons

This unifies how the buttons look in different OSs, because before we
relied in the characters being rendered by the default sans-serif font
installed in the computer.

Bug: translateselectedtext:12
Change-Id: I70e524f9664a957637f37e81465c9ec435ecc3dd
diff --git a/src/options/credits.json5 b/src/options/credits.json5
index ac911a6..286b50d 100644
--- a/src/options/credits.json5
+++ b/src/options/credits.json5
@@ -17,6 +17,12 @@
     "license": "MIT License"
   },
   {
+    "name": "@mdi/js",
+    "url": "https://materialdesignicons.com/",
+    "author": "Pictogrammers icon Group, Google LLC",
+    "license": "MIT and Apache-2.0 License"
+  },
+  {
     "name": "@polymer/paper-button",
     "url": "https://github.com/PolymerElements/paper-button",
     "author": "The Polymer Project Authors",
@@ -100,4 +106,9 @@
     "author": "Pavel Kuzmin",
     "license": "MIT License"
   },
+  {
+    "name": "Home Assistant Frontend",
+    "url": "https://github.com/home-assistant/frontend",
+    "license": "Apache-2.0 License"
+  }
 ]