fixing singularity recipe gpt4free.sif

[DaniilSarkisyan]

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My latest "community edition" of singularity on Ubuntu 22.04.1 was not able to build from "gpt4free.sif" recipe. This is how I fixed it:

1. Singularity complained about unknown section "%expose", so I changed it to

%environment
   DEBIAN_FRONTEND=noninteractive
   PORT=8501

2. I had to change

%startscript
    exec streamlit run streamlit_app.py

to

%runscript
   exec streamlit run /gpt4free/streamlit_app.py

so "streamlit" will run and find "streamlit_app.py" in the right location.