external.md: fix broken link
@@ -132,7 +132,7 @@ dependency.
By default, external dependencies are fetched as needed during `bazel build`. If
you would like to disable this behavior or prefetch dependencies, use
-[`bazel fetch`](http://docs.bazel.build/user-manual.html#fetch).
+[`bazel fetch`](https://docs.bazel.build/versions/master/command-line-reference.html#commands).
<a name="shadowing-dependencies"></a>
## Shadowing dependencies
