Test ocaml-migrate-parsetree-ocamlbuild on Travis

.travis.yml

@@ -4,15 +4,35 @@ script: bash -ex .travis-docker.sh
 services:
   - docker
 sudo: false
+
 env:
   global:
-    - PACKAGE="ocaml-migrate-parsetree"
-    - PRE_INSTALL_HOOK="cd /home/opam/opam-repository && git pull origin master && opam update -u -y"
-  matrix:
-    - DISTRO=debian-stable OCAML_VERSION=4.03.0
-    - DISTRO=debian-testing OCAML_VERSION=4.02.3
-    - DISTRO=debian-unstable OCAML_VERSION=4.04.0
-    - DISTRO=ubuntu-16.04 OCAML_VERSION=4.03.0
-    - DISTRO=alpine OCAML_VERSION=4.04.0
-    - DISTRO=alpine OCAML_VERSION=4.05.0
-    - DISTRO=alpine OCAML_VERSION=4.06.0
+  - PACKAGE="ocaml-migrate-parsetree"
+  - PRE_INSTALL_HOOK="cd /home/opam/opam-repository && git pull origin master && opam update -u -y"
+
+matrix:
+  include:
+  - env: DISTRO=debian-testing OCAML_VERSION=4.02.3
+    stage: OMP
+  - env: DISTRO=debian-stable OCAML_VERSION=4.03.0
+    stage: OMP
+  - env: DISTRO=debian-unstable OCAML_VERSION=4.04.2
+    stage: OMP
+  - env: DISTRO=ubuntu-16.04 OCAML_VERSION=4.05.0
+    stage: OMP
+  - env: DISTRO=alpine OCAML_VERSION=4.06.1
+    stage: OMP
+  - env: DISTRO=alpine OCAML_VERSION=4.07.1
+    stage: OMP
+  - env: DISTRO=debian-testing OCAML_VERSION=4.02.3 PACKAGE=ocaml-migrate-parsetree-ocamlbuild
+    stage: OMP-ocb
+  - env: DISTRO=debian-stable OCAML_VERSION=4.03.0 PACKAGE=ocaml-migrate-parsetree-ocamlbuild
+    stage: OMP-ocb
+  - env: DISTRO=debian-unstable OCAML_VERSION=4.04.2 PACKAGE=ocaml-migrate-parsetree-ocamlbuild
+    stage: OMP-ocb
+  - env: DISTRO=ubuntu-16.04 OCAML_VERSION=4.05.0 PACKAGE=ocaml-migrate-parsetree-ocamlbuild
+    stage: OMP-ocb
+  - env: DISTRO=alpine OCAML_VERSION=4.06.1 PACKAGE=ocaml-migrate-parsetree-ocamlbuild
+    stage: OMP-ocb
+  - env: DISTRO=alpine OCAML_VERSION=4.07.1 PACKAGE=ocaml-migrate-parsetree-ocamlbuild
+    stage: OMP-ocb