Tweak pronouns on English question 13 localization

Author: ThomGeG

lang/lang_en.json

@@ -59,7 +59,7 @@
     "question_10": "The means of production, such as factories and farms, must be publicly owned.",
     "question_11": "Material conditions and needs are the dominant drive behind socioeconomic changes.",
     "question_12": "Socialism can only be fully achieved in developed industrialized societies.",
-    "question_13": "''From each according to his ability, to each according to his needs'' is a good principle.",
+    "question_13": "''From each according to their ability, to each according to their needs'' is a good principle.",
     "question_14": "It is possible to peacefully convince the ruling class to conform to a socialist society.",
     "question_15": "Capitalism will induce its own demise through contradictions that result in crisis.",
     "question_16": "Class conflict is a force that has influenced much of human history.",