update dependencies

Author: Greg Bowler

composer.json

@@ -30,7 +30,7 @@
 		"g105b/phpcsv": "1.*",
 		"satooshi/php-coveralls": "0.6.*",
 
-		"phpunit/phpunit": "4.1.*",
+		"phpunit/phpunit": "^5.1",
 
 		"behat/behat": "2.*@stable",
 		"behat/mink": "@stable",