Quantiy SpecificFuelConsumption units symbols contain invalid characters

[josefprinz]

Describe the bug A clear and concise description of what the bug is.

To Reproduce Steps to reproduce the behavior (just an example):

1. Add nuget UnitsNet 4.9.0 to a .NET 4.0 project
2. Build using Visual Studio 2017 Community v15.9.2
3. See error: "foo"

Expected behavior A clear and concise description of what you expected to happen.

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Additional context Add any other context about the problem here.