Add PHP 7.2 to test matrix

And expect it to fail for now.

Signed-off-by: Michal Čihař <michal@cihar.com>

.travis.yml

@@ -50,6 +50,8 @@ matrix:
   allow_failures:
     - php: "7.0"
       env: CI_MODE=selenium
+    - php: "7.2"
+      env: CI_MODE=test
   fast_finish: true
   include:
     - php: "7.0"
@@ -58,6 +60,8 @@ matrix:
       env: CI_MODE=release
     - php: "7.0"
       env: CI_MODE=docs
+    - php: "7.2"
+      env: CI_MODE=test
 cache:
   directories:
     - $HOME/.composer/cache/