OP-551: Require behat/mink-selenium2-driver (used in behats)

Author: hmfilar

composer.json

@@ -17,6 +17,7 @@
     },
     "require-dev": {
         "behat/behat": "^3.14",
+        "behat/mink-selenium2-driver": "~1.6.0",
         "bitbag/coding-standard": "^3.0.0",
         "dmore/behat-chrome-extension": "^1.4",
         "friends-of-behat/mink": "^1.8",