Object.basename is deprecated.

Arguments to `path.basename` must be strings
```
Object.basename (/usr/share/atom/resources/app.asar/src/electron-shims.js:31:10)
Object.getHeaderText (/home/ovidiu/.atom/packages/header-42/lib/header-42.coffee:74:23)
Object.getHeader (/home/ovidiu/.atom/packages/header-42/lib/header-42.coffee:88:27)
Object.insert (/home/ovidiu/.atom/packages/header-42/lib/header-42.coffee:129:21)
atom-workspace.subscriptions.add.atom.commands.add.header-42:insert (/home/ovidiu/.atom/packages/header-42/lib/header-42.coffee:52:26)
CommandRegistry.handleCommandEvent (/usr/share/atom/resources/app.asar/src/command-registry.js:259:29)
```

Start in lib/header-42.coffee at getHeaderText around line 74, then trace the value passed to path.basename and reproduce the header insertion command in Atom. Done means the command no longer reports the basename argument error and still inserts the expected header.

Written by the indexing model from the issue text.