Bump lodash in /fixtures/packaging/systemjs-builder/prod

Bumps [lodash](https://github.com/lodash/lodash) from 4.17.4 to 4.17.21.
- [Release notes](https://github.com/lodash/lodash/releases)
- [Commits](lodash/lodash@4.17.4...4.17.21)

---
updated-dependencies:
- dependency-name: lodash
  dependency-type: indirect
...

Signed-off-by: dependabot[bot] <support@github.com>

fixtures/packaging/systemjs-builder/prod/yarn.lock

@@ -399,8 +399,8 @@ lazy-cache@^1.0.3:
   resolved "https://registry.yarnpkg.com/lazy-cache/-/lazy-cache-1.0.4.tgz#a1d78fc3a50474cb80845d3b3b6e1da49a446e8e"
 
 lodash@^4.17.4:
-  version "4.17.4"
-  resolved "https://registry.yarnpkg.com/lodash/-/lodash-4.17.4.tgz#78203a4d1c328ae1d86dca6460e369b57f4055ae"
+  version "4.17.21"
+  resolved "https://registry.yarnpkg.com/lodash/-/lodash-4.17.21.tgz#679591c564c3bffaae8454cf0b3df370c3d6911c"
 
 longest@^1.0.1:
   version "1.0.1"