Add a test for numeric-only keys
diff --git a/test/valid/key-numeric.json b/test/valid/key-numeric.json
new file mode 100644
index 0000000..862f8cb
--- /dev/null
+++ b/test/valid/key-numeric.json
@@ -0,0 +1,3 @@
+{
+    "1": {"type": "integer", "value": "1"}
+}
diff --git a/test/valid/key-numeric.toml b/test/valid/key-numeric.toml
new file mode 100644
index 0000000..532356f
--- /dev/null
+++ b/test/valid/key-numeric.toml
@@ -0,0 +1 @@
+1 = 1