Fix capitalization in article title

docs/60-schema-validation/3-validate-authors.mdx

@@ -1,4 +1,4 @@
-# 🦸‍♀️ Enable Validation for the authors Collection
+# 🦸‍♀️ Enable Validation for the Authors Collection
 
 In this exercise, you will define a JSON schema for the authors collection, apply the schema to the collection, and test the schema validation by inserting a document that does not match the schema.