No warning when unknown options are specified.

[manfred-brands]

Describe the bug
When using an typo in an option (in this case missing the trailing 's' in assemblyfilters) the report generator runs.
Expect error complaining about unknown option, instead it shows option as if it is valid.

To Reproduce

$ ~/.nuget/packages/reportgenerator/4.6.4/tools/netcoreapp3.0/ReportGenerator.exe -reporttypes:Html -targetdir:. -repor
ts:Coverage.xml -title:MyAssembly -assemblyfilter:"+myassembly.dll" 
2020-09-08T09:18:49: Arguments
2020-09-08T09:18:49:  -reporttypes:Html
2020-09-08T09:18:49:  -targetdir:.
2020-09-08T09:18:49:  -reports:Coverage.xml
2020-09-08T09:18:49:  -title:MyAssembly
2020-09-08T09:18:49:  -assemblyfilter:+myassembly.dll
2020-09-08T09:18:50: File 'D:\repos\NUnit\nunit3-vs-adapter\src\NUnitTestAdapter\AdapterSettings.cs' does not exist (any more).
...

[danielpalme]

Fixed in 16ca983.
Next release will contain the change.