doc: update yarn prerequisites

Signed-off-by: Rohan Sharma <rhnsharma5113@gmail.com>

doc/Developing.md

@@ -54,7 +54,7 @@ For Windows instructions [click here](#building-on-windows).
 
  - Node.js `>= 12.14.1` **AND** `< 13`.
    - Preferably, **use** Node version [`12.14.1`](https://nodejs.org/download/release/v12.14.1/), as it is the recommended minimum version according to the framework's supported `electron` version.
- - [Yarn package manager](https://yarnpkg.com/en/docs/install) v1.7.0
+ - [Yarn package manager](https://yarnpkg.com/en/docs/install)  `>= 1.7.0` **AND** `< 2.x.x`.
  - git (If you would like to use the Git-extension too, you will need to have git version 2.11.0 or higher.)
 
 Some additional tools and libraries are needed depending on your platform:

package.json

@@ -3,7 +3,7 @@
   "name": "@theia/monorepo",
   "version": "0.0.0",
   "engines": {
-    "yarn": "1.0.x || >=1.2.1",
+    "yarn": ">=1.7.0 <2.x.x",
     "node": ">=12.14.1 <13"
   },
   "resolutions": {