bump phpunit to 5.2

composer.json

@@ -21,7 +21,7 @@
 		"php": ">=5.6.0"
 	},
 	"require-dev": {
-		"phpunit/phpunit": "5.1.*"
+		"phpunit/phpunit": "5.2.*"
 	},
 	"suggest": {
 		"chillerlan/php-googleauth": "*"