fix(pkg): output cjs with target es2015 for older nodes

package.json

@@ -42,7 +42,7 @@
     "schema": "ts-json-schema-generator -f tsconfig.json -p 'src/{modules/**/*.ts,lib/options.ts}' -t '*' | node bin/schema-tweak.js > schema.json",
     "build": "yarn run build:esm && yarn run build:cjs && yarn run build:post",
     "build:esm": "tsc --module es2020 --outDir dist/esm",
-    "build:cjs": "tsc --module commonjs --outDir dist/cjs && sed -i 's/\"type\": \"module\",/\"type:\": \"commonjs\",/' dist/cjs/package.json",
+    "build:cjs": "tsc --module commonjs --target es2015 --outDir dist/cjs && sed -i 's/\"type\": \"module\",/\"type:\": \"commonjs\",/' dist/cjs/package.json",
     "build:post": "bin/json-transform.sh",
     "generateSchema": "yarn schema",
     "prepublishOnly": "yarn build && yarn generateSchema && yarn build:post",