Run Appveyor on more switches

Author: chambart

README.md

@@ -9,5 +9,5 @@ assert(Nullable_array.get 0 = None);
 assert(Nullable_array.get 1 = Some 4);
 ```
 
-[![Build Status](https://travis-ci.org/chambart/ocaml-nullable-array.svg)](https://travis-ci.org/chambart/ocaml-nullable-array)
-
+[![Build Status (Travis)](https://travis-ci.org/chambart/ocaml-nullable-array.svg)](https://travis-ci.org/chambart/ocaml-nullable-array)
+[![Build Status (Appveyor)](https://ci.appveyor.com/api/projects/status/github/chambart/ocaml-nullable-array&svg=true)](https://ci.appveyor.com/project/chambart/ocaml-nullable-array)

appveyor.yml

@@ -8,7 +8,11 @@ environment:
   PACKAGE: nullable-array
   TESTS: true
   matrix:
+    - OPAM_SWITCH: 4.03.0+mingw64c
+    - OPAM_SWITCH: 4.04.0+msvc64c
+    - OPAM_SWITCH: 4.04.0+mingw32c
     - OPAM_SWITCH: 4.04.0+mingw64c
+    - OPAM_SWITCH: 4.04.0+flambda+mingw64c
 
 install:
   - ps: iex ((new-object net.webclient).DownloadString("https://raw.githubusercontent.com/$env:FORK_USER/ocaml-ci-scripts/$env:FORK_BRANCH/appveyor-install.ps1"))