fix: upgrade aws-sdk from 2.1394.0 to 2.1503.0

Snyk has created this PR to upgrade aws-sdk from 2.1394.0 to 2.1503.0.

See this package in npm:
https://www.npmjs.com/package/aws-sdk

See this project in Snyk:
https://app.snyk.io/org/nft-772/project/4402cfba-bad6-45c6-8980-ba0130c2ba07?utm_source=github&utm_medium=referral&page=upgrade-pr

package.json

@@ -33,7 +33,7 @@
     "@govtechsg/oa-encryption": "^1.3.5",
     "@govtechsg/open-attestation": "^6.6.0",
     "@govtechsg/opencerts-verify": "^3.1.3",
-    "aws-sdk": "^2.590.0",
+    "aws-sdk": "^2.1503.0",
     "lodash": "^4.17.13",
     "middy": "^0.36.0",
     "node-fetch": "^2.6.1",