Use portable PDB file for SIL.Windows.Forms
Use portable PDB file for SIL.Windows.Forms

Previously nuget.org complained that symbol package validation failed
because of non-portable PDB files.

gmartin7/libpalaso,ermshiperete/libpalaso,sillsdev/libpalaso,ermshiperete/libpalaso,sillsdev/libpalaso,gmartin7/libpalaso,sillsdev/libpalaso,ermshiperete/libpalaso,sillsdev/libpalaso,gmartin7/libpalaso,ermshiperete/libpalaso,gmartin7/libpalaso