Revert "chore(deps): update dependency symbol-observable to v3 (#7299)…

…" (#7340)

This reverts commit 2809d6d,
fixing issue #7337. The problem is not the `@types/node` version, as
conjectured in #7335, but the incompatibility between the version of
`@types/node` used by Angular and our recent major update of
`symbol-observable`, which is a non-dev dependency of `@apollo/client`.

CHANGELOG.md

@@ -1,3 +1,10 @@
+## Apollo Client 3.2.7
+
+## Bug Fixes
+
+- Revert updating `symbol-observable` from version 2.x to version 3, which caused TypeScript errors with some `@types/node` versions, especially in Angular applications. <br/>
+  [@benjamn](https://github.com/benjamn) in [#7340](https://github.com/apollographql/apollo-client/pull/7340)
+
 ## Apollo Client 3.2.6
 
 ## Bug Fixes

package.json

@@ -79,7 +79,7 @@
     "hoist-non-react-statics": "^3.3.2",
     "optimism": "^0.13.0",
     "prop-types": "^15.7.2",
-    "symbol-observable": "^3.0.0",
+    "symbol-observable": "^2.0.0",
     "ts-invariant": "^0.5.0",
     "tslib": "^1.10.0",
     "zen-observable": "^0.8.14"