vcmi: adjust parseBonus and Bonus::toJson

This was an error, when scheme and parser asks different values for
source type. Corrected this.

lib/HeroBonus.cpp

@@ -1708,7 +1708,7 @@ JsonNode Bonus::toJsonNode() const
 	if(turnsRemain != 0)
 		root["turns"].Integer() = turnsRemain;
 	if(source != OTHER)
-		root["source"].String() = vstd::findKey(bonusSourceMap, source);
+		root["sourceType"].String() = vstd::findKey(bonusSourceMap, source);
 	if(sid != 0)
 		root["sourceID"].Integer() = sid;
 	if(val != 0)

lib/JsonNode.cpp

@@ -845,7 +845,7 @@ bool JsonUtils::parseBonus(const JsonNode &ability, Bonus *b)
 		}
 	}
 
-	value = &ability["source"];
+	value = &ability["sourceType"];
 	if (!value->isNull())
 		b->source = static_cast<Bonus::BonusSource>(parseByMap(bonusSourceMap, value, "source type "));