don't want to build a dot file and dot underscore file of examples directory

[nacika-ins]

I 've created a rs file to example directory using the samba from mac.
At that time, dot underscore file has been created.

I error has occurred when you run the cargo test.

$ cargo test
   Compiling kagurazaka v0.1.0 (file:///home/nacika/ws/kagurazaka)
error: "examples/._minus.rs" is not UTF-8 encoded
Could not compile `kagurazaka`.

This problem also occurs to specify the exclude to Cargo.toml.