Fix monitor.getTextScale() being doubled

Closes dan200#16. The original method divided by 2 in the getter, but that
was removed in our monitor rewrite.

Author: SquidDev

src/main/java/dan200/computercraft/shared/peripheral/monitor/MonitorPeripheral.java

@@ -243,7 +243,7 @@ public Object[] callMethod( @Nonnull IComputerAccess computer, @Nonnull ILuaCont
             case 24:
             {
                 // getTextScale
-                return new Object[] { monitor.getTextScale() };
+                return new Object[] { monitor.getTextScale() / 2.0 };
             }
         }
         return null;