Support subpath imports from externalized dependencies

Using an array of regular expressions for rollupOptions.external, I've fixed an issue causing subpath imports or external dependencies (e.g. import {} from 'pkg/subpath') to be bundled.

src/plugins/externalizeDeps.ts

@@ -33,7 +33,7 @@ export function externalizeDepsPlugin(options: ExternalOptions = {}): Plugin | n
       const defaultConfig = {
         build: {
           rollupOptions: {
-            external: [...new Set(deps)]
+            external: [...new Set(deps.map(d => new RegExp(`^${d}\/?.*`)))]
           }
         }
       }