The issues in measure-melting-point

Hi, thanks for your contribution on ScienceWorld, and I found serval issues in this.

1. The gold Path generated by `env.getGoldActionSequence()` doesn't make sense. For example:
- **action**: use thermometer in inventory on chocolate, **obs**: the thermometer measures a temperature of 34 degrees celsius。
- **action**: focus on green box, **obs**: You focus on the green box.

The generated action and the corresponding obs did not observe any change in the state of substance and directly selected the answer.

2. The problem in measuring the melting point of mercury
First, all the observation got by the gold actions still don't have a change in the state of substance, but it still choose the correct answer.
Moreover, the freezer seems very difficult to freeze the mercury to its true melting point of -35 celsius, i tried aound 50 round and it still didn't work.