qa: Add "testing" keyword to composer.json (#15)

See: php-mock/php-mock#48

Author: michalbundyra

composer.json

@@ -2,7 +2,7 @@
     "name": "php-mock/php-mock-mockery",
     "type": "library",
     "description": "Mock built-in PHP functions (e.g. time()) with Mockery. This package relies on PHP's namespace fallback policy. No further extension is needed.",
-    "keywords": ["mockery", "mock", "stub", "test double", "function", "test", "TDD", "BDD"],
+    "keywords": ["mockery", "mock", "stub", "test double", "function", "test", "testing", "TDD", "BDD"],
     "homepage": "https://github.com/php-mock/php-mock-mockery",
     "license": "WTFPL",
     "authors": [