I have the following `Berksfile` in my `app/` directory:

```
source "https://supermarket.chef.io"
cookbook "apt", "~> 3.0.0"
cookbook "nodejs", "~> 2.2"

```

When I run `berks install` (version 4.3.3), I get:

```
Resolving cookbook dependencies...
Fetching cookbook index from https://supermarket.chef.io...
Using apt (3.0.0)
...

```

My app directory contains a `Berksfile.lock` that contains the following line

```
apt (3.0.0)

```

In my initial `Berksfile` I remove the `cookbook apt` line (line 2). I expect berks to use my `Berksfile.lock`. But instead, when I run `berks install` again I get:

```
Resolving cookbook dependencies...
Fetching cookbook index from https://supermarket.chef.io...
Using apt (4.0.0)

```

And my `Berksfile.lock` gets updated with the new `apt` version. 
Is this the expected behaviour? I would expect this behaviour with the `berks update` command...