Use source-map 0.7.4

A new release of source-map was pushed 10 days ago:
https://github.com/mozilla/source-map/releases/tag/v0.7.4

It contains a fix for building on Node 18 (which was added in Oct
2020): mozilla/source-map#423.

Let's make use of it!

Author: elenatanasoiu

extensions/ql-vscode/package-lock.json

@@ -1148,6 +1148,7 @@
     "react-dom": "^17.0.2",
     "semver": "~7.3.2",
     "source-map-support": "^0.5.21",
+    "source-map": "^0.7.4",
     "stream": "^0.0.2",
     "stream-chain": "~2.2.4",
     "stream-json": "~1.7.3",