deps,tools: add missing nghttp2 license

Add `COPYING` from `nghttp2` and register it in
`tools/license-builder.sh`.

Also run `tools/license-builder.sh` and commit the
resulting `LICENSE` file.

Ref: https://github.com/nghttp2/nghttp2/blob/master/COPYING
PR-URL: https://github.com/nodejs/node/pull/14806
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Timothy Gu <timothygu99@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>

tools/license-builder.sh

@@ -80,6 +80,8 @@ addlicense "cpplint.py" "tools/cpplint.py" \
 addlicense "ESLint" "tools/eslint" "$(cat ${rootdir}/tools/eslint/LICENSE)"
 addlicense "gtest" "deps/gtest" "$(cat ${rootdir}/deps/gtest/LICENSE)"
 
+# nghttp2
+addlicense "nghttp2" "deps/nghttp2" "$(cat ${rootdir}/deps/nghttp2/COPYING)"
 
 
 mv $tmplicense $licensefile