appveyor: Update Windows FreeTDS binaries used.
appveyor: Update Windows FreeTDS binaries used.

Use latest version (0.95.81). Accomodate new upstream tarball naming
scheme.

JimDennis/pymssql,ramiro/pymssql,Aloomaio/pymssql,pymssql/pymssql,ramiro/pymssql,ramiro/pymssql,JimDennis/pymssql,pymssql/pymssql,Aloomaio/pymssql,Aloomaio/pymssql,JimDennis/pymssql