THRIFT-5158 Update Rust generator and Rust lib,test,tutorial to only support 2018 edition
Client: rs
Patch: Allen George

This closes #2078
diff --git a/lib/rs/src/transport/mem.rs b/lib/rs/src/transport/mem.rs
index 9874257..68fb265 100644
--- a/lib/rs/src/transport/mem.rs
+++ b/lib/rs/src/transport/mem.rs
@@ -139,7 +139,7 @@
 }
 
 impl TIoChannel for TBufferChannel {
-    fn split(self) -> ::Result<(ReadHalf<Self>, WriteHalf<Self>)>
+    fn split(self) -> crate::Result<(ReadHalf<Self>, WriteHalf<Self>)>
     where
         Self: Sized,
     {