Update the min requirement for Mink

Author: stof

composer.json

@@ -16,7 +16,7 @@
 
     "require": {
         "php":                  ">=5.3.6",
-        "behat/mink":           "~1.7@dev",
+        "behat/mink":           "^1.7.1@dev",
         "symfony/browser-kit":  "~2.3|~3.0",
         "symfony/dom-crawler":  "~2.3|~3.0"
     },