chore: try to make travis faster

.travis.yml

@@ -1,31 +1,15 @@
 language: c
+install: wget https://raw.githubusercontent.com/ocaml/ocaml-ci-scripts/master/.travis-docker.sh
+script: bash -ex .travis-docker.sh
+services:
+- docker
 env:
-  - OCAML_VERSION=4.02.3
-  - OCAML_VERSION=4.05.0
-  - OCAML_VERSION=4.05.0+flambda
-  - OCAML_VERSION=4.06.0
-addons:
-  apt:
-    sources:
-      - avsm
-    packages:
-      - opam
-# Caching may take a lot of space with so many ocaml versions
-cache:
-  directories:
-    - $HOME/.opam
-before_install:
-  # Some opam boilerplate
-  - export OPAMYES=1
-  - export OPAMVERBOSE=1
-  - opam init
-  - opam switch ${OCAML_VERSION}
-  - eval `opam config env`
-install:
-  # Install dependencies
-  - opam pin add --no-action sequence .
-  - opam install jbuilder base-bytes result
-script:
-  - make build
-  - opam install qcheck qtest
-  - make test
+  global:
+  - PINS="sequence:."
+  - DISTRO="ubuntu-16.04"
+  matrix:
+  - PACKAGE="sequence" OCAML_VERSION="4.02.3" DEPOPTS="base-bigarray"
+  - PACKAGE="sequence" OCAML_VERSION="4.03.0" DEPOPTS="base-bigarray"
+  - PACKAGE="sequence" OCAML_VERSION="4.04.2" DEPOPTS="base-bigarray"
+  - PACKAGE="sequence" OCAML_VERSION="4.05.0" DEPOPTS="base-bigarray"
+  - PACKAGE="sequence" OCAML_VERSION="4.06.0" DEPOPTS="base-bigarray"

sequence.opam

@@ -25,7 +25,6 @@ depends: [
   "qcheck" {test}
   "qtest" {test}
   "odoc" {doc}
-  "ocaml-version" { >= "4.02" }
 ]
 tags: [ "sequence" "iterator" "iter" "fold" ]
 homepage: "https://github.com/c-cube/sequence/"