Declare svelte and svelte-loader as optional dependencies

Version 5.3.0 added the peer dependency declaration but forgot to mark it as optional (while the implementation already treats it as optional)

Author: stof

package.json

@@ -200,6 +200,12 @@
     "stylus-loader": {
       "optional": true
     },
+    "svelte": {
+      "optional": true
+    },
+    "svelte-loader": {
+      "optional": true
+    },
     "ts-loader": {
       "optional": true
     },