Cleaner way to install opam in travis CI

.travis-ci.sh

@@ -1,16 +1,15 @@
 # Edit this for your own project dependencies
 OPAM_DEPENDS="ocamlfind ocamlbuild"
 
-echo "yes" | sudo add-apt-repository ppa:avsm/ocaml42+opam12
-sudo apt-get update -qq
-sudo apt-get install -qq ocaml ocaml-native-compilers camlp4-extra opam
 export OPAMYES=1
 export OPAMVERBOSE=1
+
 opam init
 opam switch ${OCAML_VERSION}
 eval `opam config env`
 opam install ${OPAM_DEPENDS}
 eval `opam config env`
+
 make lib
 make bin
 make test

.travis.yml

@@ -1,6 +1,10 @@
 language: c
 sudo: required
 script: bash -ex .travis-ci.sh
+before_install:
+  - echo "yes" | sudo add-apt-repository ppa:avsm/ocaml42+opam12
+  - sudo apt-get update -qq
+  - sudo apt-get install -qq ocaml ocaml-native-compilers camlp4-extra opam
 env:
   - OCAML_VERSION=4.00.1
   - OCAML_VERSION=4.01.0