External Libraries: Update some external libraries.

This updates three external libraries to their latest versions:

- `backbone` from `1.4.0` to `1.4.1`.
- `underscore` from `1.13.1` to `1.13.2`.
- `clipboard` from `2.0.8` to `2.0.10`.

These are all minor updates containing bug fixes and documentation improvements.

See #55547.

git-svn-id: https://develop.svn.wordpress.org/trunk@53164 602fd350-edb4-49c9-b593-d223f7449a82

package.json

@@ -130,8 +130,8 @@
 		"@wordpress/warning": "2.6.0",
 		"@wordpress/widgets": "2.4.1",
 		"@wordpress/wordcount": "3.6.0",
-		"backbone": "1.4.0",
-		"clipboard": "2.0.8",
+		"backbone": "1.4.1",
+		"clipboard": "2.0.10",
 		"core-js-url-browser": "3.6.4",
 		"element-closest": "^2.0.2",
 		"formdata-polyfill": "4.0.0",
@@ -150,7 +150,7 @@
 		"react-dom": "17.0.2",
 		"regenerator-runtime": "0.13.9",
 		"twemoji": "14.0.2",
-		"underscore": "1.13.1",
+		"underscore": "1.13.2",
 		"whatwg-fetch": "3.6.2"
 	},
 	"scripts": {