Use "unix" attribute views for UNIX configuration

[electrum]

What is the reason that Configuration.unix() uses setAttributeViews("basic") rather than setAttributeViews("unix")? This would match the behavior of the JDK UNIX file system provider. I'm happy to send a patch if this change is desired.

[chaoren]

See

jimfs/jimfs/src/main/java/com/google/common/jimfs/Configuration.java

Lines 68 to 69 in c2e8e1f

	* <li>supports only the {@linkplain BasicFileAttributeView basic} file attribute view, to avoid
	* overhead for unneeded attributes

and

jimfs/jimfs/src/main/java/com/google/common/jimfs/Configuration.java

Lines 74 to 83 in c2e8e1f

	* <p>To create a modified version of this configuration, such as to include the full set of UNIX
	* file attribute views, {@linkplain #toBuilder() create a builder}.
	*
	* <p>Example:
	*
	* <pre>
	* Configuration config = Configuration.unix().toBuilder()
	* .setAttributeViews("basic", "owner", "posix", "unix")
	* .setWorkingDirectory("/home/user")
	* .build(); </pre>