Bump Gutenberg reference to 5194cdb

[fluiddot]

Bumps the Gutenberg reference to 5194cdb.

This PR includes three fixes that were required to include recent changes from Gutenberg repo:

1. Disable NPM version 7 - Disable NPM version 7 #3307
2. Fix: Size setting is not displayed - [RNMobile] Image block: Use image default size from settings WordPress/gutenberg#30186
3. Update the package-lock.json file due to recent changes in gutenberg/package.json.

To test:
For testing this PR, verify first that the installed NPM version is version 6.x.

1. Run npm install.
2. Verify that the package-lock.json file remains unchanged.

PR submission checklist:

• I have considered adding unit tests where possible.
• I have considered if this change warrants user-facing release notes more info and have added them to RELEASE-NOTES.txt if necessary.

[dcalhoun]

LGTM. The demo app runs successfully on the iOS simulator. The package-lock.json remains unchanged after npm install, aside from the wp-prettier change, which I believe is a completely separate issue.

[fluiddot]

LGTM. The demo app runs successfully on the iOS simulator. The package-lock.json remains unchanged after npm install, aside from the wp-prettier change, which I believe is a completely separate issue.

I have this same issue from time to time, the way I usually fix it is by deleting all the node_modules folders and installing the dependencies again:

1. rm -rf node_modules
2. cd gutenberg && npm run distclean
3. npm install [in gutenberg-mobile project folder]

Thank you very much for the review 🙇 !