Bump to v1.60.0 RSVP due to protobuf 3.1 req

protobuf uses spare_capacity_mut on vectors that was stabilized in 1.60
rust-lang/rust#93016

Author: nyurik

.appveyor.yml

@@ -16,7 +16,7 @@ environment:
       target: x86_64-pc-windows-msvc
     - channel: stable
       target: i686-pc-windows-msvc
-    - channel: 1.58.0
+    - channel: 1.60.0
       target: x86_64-pc-windows-msvc
 
 install: