Update README to use Docker image used in CI.

Author: niting

README.md

@@ -38,10 +38,10 @@ docker run --device=/dev/kvm \
            -it \
            --security-opt seccomp=unconfined \
            --volume $(pwd)/kvm-ioctls:/kvm-ioctls \
-           rustvmm/dev:v2
+           rustvmm/dev:v5
 cd kvm-ioctls/
 cargo test
 ```
 
 For more details about the integration tests that are run for `kvm-ioctls`,
-check the [rust-vmm-ci](https://github.com/rust-vmm/rust-vmm-ci) readme.
+check the [rust-vmm-ci](https://github.com/rust-vmm/rust-vmm-ci) readme.