bump std++ to fix build

55711e8e · Ralf Jung · 84ee5362 · 55711e8e
Commit 55711e8e authored Apr 18, 2018 by Ralf Jung
--- a/opam
+++ b/opam
@@ -11,5 +11,5 @@ install: [make "install"]
 remove: ["rm" "-rf" "%{lib}%/coq/user-contrib/iris"]
 depends: [
  "coq" { (>= "8.7.1" & < "8.9~") | (= "dev") }
-  "coq-stdpp" { (= "dev.2018-04-06.0") | (= "dev") }
+  "coq-stdpp" { (= "dev.2018-04-18.1.e54646d4") | (= "dev") }
 ]