ensuring all PHP versions use the same phpunit from composer in travis CI and documented this alternative in the README

.travis.yml

@@ -9,7 +9,7 @@ before_script:
   - composer install -n
 
 script:
-  - cd tst && phpunit
+  - cd tst && ../vendor/phpunit/phpunit/phpunit
 
 after_script:
   - cd ..

tst/README.md

@@ -23,6 +23,12 @@ $ cd PrivateBin/tst
 $ phpunit
 ```
 
+Or you can also use the phpunit installed as dependency of eris by composer:
+```console
+$ cd PrivateBin/tst
+$ ../vendor/phpunit/phpunit/phpunit
+```
+
 Running JavaScript unit tests
 =============================