feat: add subject-leading-capital rule

Author: marionebl

source/rules/subject-leading-capital.js

@@ -0,0 +1,17 @@
+import ensureCase from '../library/ensure-case';
+
+export default (parsed, when, value) => {
+	const negated = when === 'never';
+	const {subject} = parsed;
+	const result = ensureCase(subject[0], value);
+	return [
+		negated ? !result : result,
+		[
+			`message must`,
+			negated ? `not` : null,
+			`be ${value}`
+		]
+		.filter(Boolean)
+		.join(' ')
+	];
+};