Fix postinstall script for Windows

[louiszawadzki]

What does this PR do?

Fixes#358
Executes the postinstall script without any slash in the command.
There are different ways to execute the script, the solution is the only one I found working for *nix and windows:

scripts/replace-react-require.js

• ✅ *nix
• ❌ Windows: slashes make it fail

./replace-react-require.js (moving the file at the root)

• ✅ *nix
• ❌ Windows: slashes make it fail

replace-react-require.js

• ❌ *nix: interpreted as a command, not executing script
• ✅ Windows

node scripts/replace-react-require.js or node replace-react-require.js

• ✅ *nix
• ✅ Windows

Motivation

Additional Notes

Anything else we should know when reviewing?

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests
• Make sure you discussed the feature or bugfix with the maintaining team in an Issue
• Make sure each commit and the PR mention the Issue number (cf the CONTRIBUTING doc)
• If this PR is auto-generated, please make sure also to manually update the code related to the change