Update Russian translation

Author: solokot

_locales/ru/messages.json

@@ -580,7 +580,7 @@
 		"description": "Title of the button 'apply the system theme when formatting a page'"
 	},
 	"optionContentWidth": {
-		"message": "content width when formatting a page (em)",
+		"message": "ширина содержимого при форматировании страницы (em)",
 		"description": "Options page label: 'content width when formatting a page (em)'"
 	},
 	"optionWarnUnsavedPage": {
@@ -1051,4 +1051,4 @@
 		"message": "Неправильный JSON",
 		"description": "Options editor error message: 'Invalid JSON'"
 	}
-}
+}