Fixes #2341, fixes #2317: moved codeception dependecies to "suggest" section, fixed codeception version on stable branch

composer.json

@@ -21,12 +21,14 @@
 	},
 	"require-dev": {
 		"yiisoft/yii2-codeception": "*",
-		"codeception/codeception": "*",
-		"codeception/specify": "*",
-		"codeception/verify": "*",
 		"yiisoft/yii2-debug": "*",
 		"yiisoft/yii2-gii": "*"
 	},
+	"suggest": {
+		"codeception/codeception": "1.8.*@dev",
+		"codeception/specify": "*",
+		"codeception/verify": "*"
+	},
 	"scripts": {
 		"post-create-project-cmd": [
 			"yii\\composer\\Installer::setPermission"