Switch from toml to tomli for TOML v1 compat (#622)

* Switch from `toml` to `tomli` for TOML v1 compat

* Fix docs build by adding upper pinning to Sphinx

docs/requirements-docs.txt

@@ -1,4 +1,4 @@
 myst-parser>=0.12.0
-Sphinx>=3.2.0
+Sphinx>=3.2.0,<4.1.0
 sphinx-copybutton>=0.3.0
 sphinx-rtd-theme>=0.5.0

nbqa/__main__.py

@@ -19,7 +19,7 @@
     Tuple,
 )
 
-import toml
+import tomli
 from pkg_resources import parse_version
 
 from nbqa import replace_source, save_source
@@ -309,9 +309,10 @@ def _get_configs(cli_args: CLIArgs, project_root: Path) -> Configs:
     config = get_default_config()
 
     # If a section is in pyproject.toml, use that.
-    if (project_root / "pyproject.toml").is_file():
+    pyproject_path = project_root / "pyproject.toml"
+    if pyproject_path.is_file():
 
-        config_file = toml.load(str(project_root / "pyproject.toml"))
+        config_file = tomli.loads(pyproject_path.read_text("utf-8"))
         if "tool" in config_file and "nbqa" in config_file["tool"]:
             file_config = config_file["tool"]["nbqa"]
             for section in config:

setup.cfg

@@ -35,7 +35,7 @@ py_modules = nbqa
 install_requires =
     ipython>=7.8.0
     tokenize-rt>=3.2.0
-    toml
+    tomli<2.0.0
     importlib_metadata;python_version < '3.8'
 python_requires = >=3.6.0