build: enable emitDecoratorMetadata

tsconfig.spec.json

@@ -4,7 +4,8 @@
         "outDir": "../out-tsc/spec",
         "baseUrl": "./",
         "types": ["jest", "node"],
-        "experimentalDecorators": true
+        "experimentalDecorators": true,
+        "emitDecoratorMetadata": true
     },
     "files": ["src/polyfills.ts"],
     "include": ["**/*.spec.ts", "**/*.d.ts"]