use specific Coq and ssreflect versions for Travis

Author: palmskog

.travis-ci.sh

@@ -1,13 +1,13 @@
 opam init --yes --no-setup
 eval $(opam config env)
 opam repo add coq-released https://coq.inria.fr/opam/released
-opam install coq --yes
+opam install coq.$COQ_VERSION --yes --verbose
 
 ./build.sh
 
 case $DOWNSTREAM in
 verdi)
-  opam install coq-mathcomp-ssreflect --yes
+  opam install coq-mathcomp-ssreflect.$SSREFLECT_VERSION --yes --verbose
 
   pushd ..
     git clone 'http://github.com/uwplse/StructTact'

.travis.yml

@@ -8,8 +8,12 @@ addons:
       - ocaml
       - opam
 env:
-  - DOWNSTREAM=none
-  - DOWNSTREAM=verdi
+  global:
+    - COQ_VERSION=8.5.3
+    - SSREFLECT_VERSION=1.6
+  matrix:
+    - DOWNSTREAM=none
+    - DOWNSTREAM=verdi
 sudo: false
 notifications:
   email: false