Run tests in travis

Running tests was removed from make target all in
https://github.com/eproxus/meck/commit/30a116a7
diff --git a/.travis.yml b/.travis.yml
index 7263010..598ec91 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -9,4 +9,4 @@
   - R16B03-1
   - R15B03
 before_script: "make get-deps"
-script: "make all"
+script: "make test"