fix vulnerability using dotnet command if nuget not exist

Is your feature request related to a problem? Please describe.
I'm using frogbot inside a docker that does not have nuget but uses dotnet commands.
when I run it I get:

Cloning repository with these details:
Clone url: [https://gitlab-ci-token:[MASKED]@gitlab.xxxx.net/develop/services/devops-xxxx.git](https://gitlab-ci-token:%5BMASKED%5D@gitlab.xxxx.net/develop/services/devops-xxxx.git) remote name: origin, branch: refs/heads/develop
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Start fixing Microsoft.NETCore.App with 2.0.3
Creating branch: frogbot-Microsoft.NETCore.App-1da05d022e80e8fb1bff4c48ea5bf8fe
[Warn] failed while fixing Microsoft.NETCore.App with version: 2.0.3 with error: 
nuget  microsoft.netcore.app2.0.3 command failed: exec: "nuget": executable file not found in $PATH
[Info] Running git checkout to base branch: develop

Describe the solution you'd like to see
I would like it to use dotnet command instead of nuget

Start by reproducing the reported vulnerability-fix flow in a Docker environment without nuget, using the logged Microsoft.NETCore.App 2.0.3 case. Trace where the failed nuget command is selected, then confirm the fix path can use a dotnet command and completes without the executable-not-found error.