Update tar-fs to resolve security warnings

This also installs a slightly older version of tar-stream, as the latest
uses a very new version of bl, which drops support for older Node
versions. We don't explicitly declare our engine support, but it'd be
good to nice to keep whilst we can.

Author: pimterry

package-lock.json

@@ -24,7 +24,8 @@
   },
   "homepage": "https://github.com/pimterry/lambda-git#readme",
   "dependencies": {
-    "tar-fs": "^1.14.0"
+    "tar-fs": "^2.1.0",
+    "tar-stream": "~2.0.1"
   },
   "devDependencies": {
     "bats": "^0.4.2",