updated to zipperposition-2.0 and ocaml-4.07, which is required for it;

--- a/etc/settings	Wed Dec 16 16:30:04 2020 +0100
+++ b/etc/settings	Wed Dec 16 16:56:07 2020 +0100
@@ -150,7 +150,7 @@
 
 ISABELLE_OPAM_ROOT="$USER_HOME/.opam"
 
-ISABELLE_OCAML_VERSION="ocaml-base-compiler.4.05.0"
+ISABELLE_OCAML_VERSION="ocaml-base-compiler.4.07.0"
 
 
 ###

--- a/src/Pure/Admin/build_zipperposition.scala	Wed Dec 16 16:30:04 2020 +0100
+++ b/src/Pure/Admin/build_zipperposition.scala	Wed Dec 16 16:56:07 2020 +0100
@@ -9,7 +9,7 @@
 
 object Build_Zipperposition
 {
-  val default_version = "1.6"
+  val default_version = "2.0"
 
 
   /* build Zipperposition */