Make json5 description capitalization consistent with other links

Author: dtolnay

_src/README.md

@@ -56,7 +56,7 @@ Serde by the community.
 - [BSON], the data storage and network transfer format used by MongoDB.
 - [Avro], a binary format used within Apache Hadoop, with support for schema
   definition.
-- [JSON5], A superset of JSON including some productions from ES5.
+- [JSON5], a superset of JSON including some productions from ES5.
 - [Postcard], a no\_std and embedded-systems friendly compact binary format.
 - [URL] query strings, in the x-www-form-urlencoded format.
 - [Envy], a way to deserialize environment variables into Rust structs.