Set doc_cfg on docs.rs builds

Author: t4lz

src/lib.rs

@@ -11,6 +11,8 @@
 // Adapted from rustc's path_relative_from
 // https://github.com/rust-lang/rust/blob/e1d0de82cc40b666b88d4a6d2c9dcbc81d7ed27f/src/librustc_back/rpath.rs#L116-L158
 
+#![cfg_attr(docsrs, feature(doc_cfg))]
+
 use std::path::*;
 
 /// Construct a relative path from a provided base directory path to the provided path.