Can't run sample code in colab

**Describe the bug**
1. Running FinRL_Ensemble_StockTrading_ICAIF_2020.ipynb on colab, there is an error ModuleNotFoundError: No module named 'finrl'.

2. Running !pip install git+https：//github.com/AI4Finance-Foundation/FinRL.git, there is an error Collecting gym==0.21 Using cached gym-0.21.0.tar.gz error：subprocess-exited-with-error × python setup.py egg_info did not run successfully. │ exit code：1 ╰─> See above for output. note：This error originates from a subprocess，and is likely not a problem with pip. Preparing metadata ... error error：metadata-generation-failed × Encountered error while generating package metadata. ╰─> See above for output. note：This is an issue with the package mentioned above，not pip. hint：See above for details.

**To Reproduce**
Steps to reproduce the behavior:
1. Running FinRL_Ensemble_StockTrading_ICAIF_2020.ipynb on colab
2. there is an error ModuleNotFoundError: No module named 'finrl'.

**Expected behavior**
A clear and concise description of what you expected to happen.

**Screenshots**
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**Desktop (please complete the following information):**
- OS: [e.g. iOS]
- Browser [e.g. chrome, safari]
- Version [e.g. 22]

**Smartphone (please complete the following information):**
- Device: [e.g. iPhone6]
- OS: [e.g. iOS8.1]
- Browser [e.g. stock browser, safari]
- Version [e.g. 22]

**Additional context**
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