Update ruby-magic-static to v0.3.5

This pulls in https://github.com/kwilczynski/ruby-magic/pull/5, which brings significant improvements in the building of libmagic:

• Use mini_portile2 gem to build the C extension.
• Clean up unneeded files after build.
• By default, build a static library of libmagic and link it.
• Support disabling of static library generation via the --disable-static argument.
• Support for using the system library via the --use-system-libraries argument.