docs(blog) : compilation.cache is deprecated now (#4302)

* Docs(blog) : compilation.cache is deprecated now

* Update src/content/blog/2020-10-10-webpack-5-release.md

Co-authored-by: Sam Chen <chenxsan@gmail.com>

Author: jeffin143

src/content/blog/2020-10-10-webpack-5-release.md

@@ -1251,6 +1251,7 @@ These dependencies are cheaper to process and webpack uses them when possible
 - `ChunkGraph` added
 - `ChunkGroup.setParents` removed
 - `ChunkGroup.containsModule` removed
+- `Compilation.cache` was removed in favor of `Compilation.getCache()`
 - `ChunkGroup.remove` no longer disconnected the group from block
 - `ChunkGroup.compareTo` signature changed
 - `ChunkGroup.getChildrenByOrders` signature changed