fix(webpack-config): loosen peer dependency versions

[byCedric]

Why

This allows npm to install @expo/webpack-config@19 on a SDK 50 project, even though it's currently in maintenance mode.

I tested this in a separate blank project, seems to work fine.

⚠️ Apparently, we have some issues with the x.x.x-preview.x versions. npm won't allow 50.0.0-preview.11 when setting version constraint to >=49.0.7, which seems weird to me as 50.0.0-preview.11 is in-fact higher than 49.0.7. ℹ️ This is now resolved by using ^50.0.0-0 to force-allow prereleases as peer dependency, see this thread

How

• Loosened peer dependency constraint
• Tested it in blank test project

Test Plan

ℹ️ Test this change with a tarball, not with the file:... option as that doesn't install or validate the peer dependencies properly with npm.

Create a test build for @expo/webpack-config

• $ git clone <this repo>
• $ cd <this repo>
• $ yarn && yarn build
• $ cd ./packages/webpack-config
• $ npm pack

Create a test project

• $ npm create expo -- "./test-webpack" --template blank@beta
• $ cd ./test-webpack
• Copy over the *.tar.gz file from <this repo>/packages/webpack-config/*.tar.gz
• Add "@expo/webpack-config": "./*.tar.gz" to package.json (use exact file name of the tar file)
• $ npm install
• $ npm run web
  • Install the missing react-native-web and react-dom packages
• $ npm run web
  • This should work fine.