Require specific version on Mockery

More recent versions break things due to Hamcrest

See mockery/mockery#464

Author: gmazzap

composer.json

@@ -31,7 +31,8 @@
         "antecedent/patchwork": "1.3.*"
     },
     "require-dev": {
-        "phpunit/phpunit": "~4.4"
+        "phpunit/phpunit": "~4.8",
+        "mockery/mockery": "0.9.3"
     },
     "autoload": {
         "psr-4": {