Add phar building to Travis-CI

Author: defuse

.travis.yml

@@ -12,6 +12,11 @@ matrix:
 
 install:
     - composer install
+    - curl -LSs https://box-project.github.io/box2/installer.php | php
+    - mkdir ~/box
+    - mv box.phar ~/box/box
 
 script:
     - ./test.sh
+    - PATH=$PATH:~/box/ make -C dist/ build-phar
+    - ./test.sh dist/defuse-crypto.phar