Rust: fix typo in README.md

Author: nickrolfe

rust/ast-generator/README.md

@@ -8,7 +8,7 @@ It uses:
 Both are fetched by bazel while building. In order to have proper IDE support and being
 able to run cargo tooling in this crate, you can run
 ```bash
-bazel run //rust/ast-generator:inject_sources
+bazel run //rust/ast-generator:inject-sources
 ```
 which will create the missing sources. Be aware that bazel will still use the source taken
 directly from `rust-analyzer`, not the one in your working copy. Those should not need to be