Switch from deprecated "toml" library

Fixes #451

setup.py

@@ -45,7 +45,7 @@
         "picosvg>=0.20.4",
         "pillow>=7.2.0",
         "regex>=2020.4.4",
-        "toml>=0.10.1",
+        "tomlkit",
         "ufo2ft[cffsubr]>=2.24.0",
         "ufoLib2>=0.6.2",
         "resvg-cli>=0.22.0.post3",

src/nanoemoji/config.py

@@ -20,9 +20,9 @@
     import importlib_resources as resources  # pytype: disable=import-error
 
 import itertools
+import tomlkit
 from pathlib import Path
 from picosvg.svg_transform import Affine2D
-import toml
 from typing import Any, Iterable, MutableMapping, NamedTuple, Optional, Tuple, Sequence
 
 from nanoemoji import util
@@ -288,7 +288,8 @@ def write(dest: Path, config: FontConfig):
             for m in config.masters
         },
     }
-    dest.write_text(toml.dumps(toml_cfg))
+    toml_cfg = {key: val for key, val in toml_cfg.items() if val is not None}
+    dest.write_text(tomlkit.dumps(toml_cfg))
 
 
 def _resolve_config(
@@ -297,8 +298,8 @@ def _resolve_config(
     if config_file is None:
         with resources.path("nanoemoji.data", _DEFAULT_CONFIG_FILE) as config_file:
             # no config_dir in this context; bad input if we need it
-            return None, toml.load(config_file)
-    return config_file.parent, toml.load(config_file)
+            return None, tomlkit.load(open(config_file))
+    return config_file.parent, tomlkit.load(open(config_file))
 
 
 def _resolve_src(relative_base: Optional[Path], src: str) -> Iterable[Path]: