Set all documentation examples to 2018 edition
diff --git a/src/path.rs b/src/path.rs
index f35c111..10a043e 100644
--- a/src/path.rs
+++ b/src/path.rs
@@ -358,7 +358,7 @@
         ///
         /// # Example
         ///
-        /// ```
+        /// ```edition2018
         /// use syn::{Path, Result, Token};
         /// use syn::parse::{Parse, ParseStream};
         ///