chore(package.json): bump engines to node >=12.0.0 (smithy-lang#481)

Author: trivikr

smithy-typescript-codegen/src/main/resources/software/amazon/smithy/typescript/codegen/base-package.json

@@ -30,7 +30,7 @@
     "typescript": "~4.1.2"
   },
   "engines": {
-    "node": ">=10.0.0"
+    "node": ">=12.0.0"
   },
   "typesVersions": {
     "<4.0": {