ci: TS 4.0 is now the minimum version

Author: cyrilletuzi

.github/workflows/main.yml

@@ -79,7 +79,7 @@ jobs:
     - name: Build the lib (with the current version, as it is what is published on npm)
       run: npm run build
     - name: Downgrade dependencies to minimal required version
-      run: npm install typescript@3.9.2 [email protected] [email protected] [email protected] @angular/[email protected] @angular/[email protected] @angular/[email protected] @angular/[email protected] @angular/[email protected] @angular/[email protected] @angular/[email protected] @angular/[email protected] @angular-devkit/[email protected]
+      run: npm install typescript@4.0.2 [email protected] [email protected] [email protected] @angular/[email protected] @angular/[email protected] @angular/[email protected] @angular/[email protected] @angular/[email protected] @angular/[email protected] @angular/[email protected] @angular/[email protected] @angular-devkit/[email protected]
       env:
         CI: true
     - name: Run unit tests