nimble should not prompt for "X already exists. Overwrite?" when X is just a dependency
after:
```
git clone https://github.com/dom96/choosenim
cd choosenim
nimble build
```

I got:

```
  Verifying dependencies for choosenim@0.3.2
 Installing nimble@>= 0.8.5
Downloading https://github.com/nim-lang/nimble using git
  Verifying dependencies for nimble@0.8.10
      Info: Dependency on compiler@#head already satisfied
  Verifying dependencies for compiler@#head
 Installing nimble@0.8.10
   Building nimble/nimble using c backend
   Success: nimble installed successfully.
 Installing untar@>= 0.1.0
Downloading https://github.com/dom96/untar using git
  Verifying dependencies for untar@0.1.0
 Installing untar@0.1.0
   Success: untar installed successfully.
 Installing libcurl@>= 1.0.0
Downloading https://github.com/Araq/libcurl using git
  Verifying dependencies for libcurl@1.0.0
 Installing libcurl@1.0.0
   Success: libcurl installed successfully.
 Installing analytics@>= 0.1.0
Downloading https://github.com/dom96/analytics using git
  Verifying dependencies for analytics@0.1.0
 Installing uuids@>= 0.1.7
Downloading https://github.com/pragmagic/uuids using git
   Warning: Package 'uuids' has an incorrect structure. The top level of the package source directory should contain at most one module, named 'uuids.nim', but a file named 'urandom.nim' was found. This will be an error in the future.
      Hint: If this is the primary source file in the package, rename it to 'uuids.nim'. If it's a source file required by the main module, or if it is one of several modules exposed by 'uuids', then move it into a 'uuids/' subdirectory. If it's a test file or otherwise not required to build the the package 'uuids.nim', prevent its installation by adding `skipFiles = @["urandom.nim"]` to the .nimble file. See https://github.com/nim-lang/nimble#libraries for more info.
  Verifying dependencies for uuids@0.1.9
 Installing isaac@>= 0.1.3
Downloading https://github.com/pragmagic/isaac using git
  Verifying dependencies for isaac@0.1.3
 Installing isaac@0.1.3
   Success: isaac installed successfully.
 Installing uuids@0.1.9
   Success: uuids installed successfully.
 Installing osinfo@>= 0.2.0
Downloading https://github.com/nim-lang/osinfo.git using git
  Verifying dependencies for osinfo@0.2.0
 Installing osinfo@0.2.0
   Success: osinfo installed successfully.
 Installing analytics@0.1.0
   Success: analytics installed successfully.
 Installing osinfo@>= 0.2.0
Downloading https://github.com/nim-lang/osinfo.git using git
  Verifying dependencies for osinfo@0.2.0
 Installing osinfo@0.2.0
    Prompt: osinfo@0.2.0 already exists. Overwrite? [y/N]
    Answer: y
   Success: osinfo installed successfully.
   Building choosenim/choosenim using c backend

```

Why should nimble ask for "Prompt: osinfo@0.2.0 already exists. Overwrite? [y/N]" ? 
I understand it should ask if I'm explicitly calling `nimble install osinfo` but here I was just calling `nimble install X` where X depends on osinfo