fix setuptools_scm LookupError bug
If setuptools_scm is installed but gwinc is not called from the gwinc directory, a LookupError was previously thrown. Now the version is set to '?.?.?' in this case.
If setuptools_scm is installed but gwinc is not called from the gwinc directory, a LookupError was previously thrown. Now the version is set to '?.?.?' in this case.