Address more PR feedback

- Add libssl-dev dependency to DockerFile, because the package upgrade test still depend on this. It can be removed once a newer package without libssl-dev dependency is uploaded.
- Check pre-reqs in the package script.

scripts/dotnet-cli-build/InstallerTargets.cs

@@ -45,9 +45,10 @@ namespace Microsoft.DotNet.Cli.Build
             var version = c.BuildContext.Get<BuildVersion>("BuildVersion").SimpleVersion;
             var debFile = c.BuildContext.Get<string>("InstallerFile");
             var manPagesDir = Path.Combine(Dirs.RepoRoot, "Documentation", "manpages");
+            var previousVersionURL = $"https://dotnetcli.blob.core.windows.net/dotnet/{channel}/Installers/Latest/dotnet-ubuntu-x64.latest.deb";
 
             Cmd(Path.Combine(Dirs.RepoRoot, "scripts", "package", "package-debian.sh"),
-                "-v", version, "-i", Dirs.Stage2, "-o", debFile, "-p", packageName, "-m", manPagesDir, "-c", channel)
+                "-v", version, "-i", Dirs.Stage2, "-o", debFile, "-p", packageName, "-m", manPagesDir, "--previous-version-url", previousVersionURL)
                     .Execute()
                     .EnsureSuccessful();
             return c.Success();

scripts/dotnet-cli-build/Utils/Monikers.cs

@@ -33,7 +33,6 @@ namespace Microsoft.DotNet.Cli.Build
                     break;
                default:
                     throw new Exception($"Unknown channel - {channel}");
-                    break;
             }
 
             return packageName;