fix bad merge

(see https://github.com/gildas-lormeau/SingleFile/pull/1717/)

_locales/pl/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": "szerokość zawartości podczas formatowania strony (em)",
 		"description": "Options page label: 'content width when formatting a page (em)'"
 	},
 	"optionWarnUnsavedPage": {