Black config not added to pyproject.toml when updating template_config.yml

Steps to reproduce:
1. plugin with black disable (i.e. pulp python)
2. edit template_config.yml `black: true`
3. run `./plugin-template --github pulp_python`

act: 
no configuration section added for black in pyprject.toml

exp:
pyproject.toml contains black configuration section
```
[tool.black]
line-length = 100
``` 