update CHANGES and fix the version calculation for the error changes

Author: avsm

CHANGES.md

@@ -1,3 +1,12 @@
+v5.1.1 2019-11-23
+-----------------
+
+This is a point release to fix a regression in 5.1.0
+on compilers earlier than 4.07.
+
+The release also fixes the test suite and CI on compilers
+greater than 4.07.
+
 v5.1.0 2019-11-23
 -----------------
 

ppx_test/errors/pp.ml

@@ -3,7 +3,7 @@
 external sys_exit : int -> 'a = "caml_sys_exit"
 let () = at_exit (fun () -> sys_exit 0)
 
-#if OCAML_VERSION >= (4,7,0)
+#if OCAML_VERSION >= (4,8,0)
 let () = Clflags.(error_style := Some Short)
 #endif