Added NormaliseLineEndingsForTextFilesAttribute to fix line ending issue...

...s inside approval tests

I have hit this issue so many times with git and line endings and it is painful to fix retrospectively (in terms of fixing the git repo). Also teamcity does not respect .gitattributes which means the binary trick does not always work.

By introducing this attribute I can simply go `[assembly: NormaliseLineEndingsForTextFiles]` in my assemblyinfo.cs and all my line ending woes will just go away :)

What do you think?