Ignore hidden files in precompile and build commands (fix #4)

Hi @rpflorence,

here’s my fix for skipping hidden files.

I didn’t add tests since I didn’t know what strategy you would like to take for this.

I thought I could create a fake hidden file in build.js in the `create` function so that after building `assertFilesMatch('index.js');` would catch any errors.

Let me know what you think!