Update codecs.md

Fix typo

Author: xcoulon

docs/reference/content/bson/codecs.md

@@ -98,7 +98,7 @@ The `DocumentCodec`, because it is constructed with a `CodecRegistry`, can now u
 values contained in each Document that it encodes.
 
 One more problem remains, however.  Consider the problem of encoding values to a BSON DateTime.  An application may want  to 
-encode to a BSON DateTime instances of both the original Java `Date` class as well as the Java 8 `Instance` class.  It's easy to create 
+encode to a BSON DateTime instances of both the original Java `Date` class as well as the Java 8 `Instant` class.  It's easy to create 
 implemenations of `Codec<Date>` and `Codec<Instant>`, and either one can be used for encoding.  But when decoding, a Document `Codec` 
 also has to choose which Java type to decode a BSON DateTime to.  Rather than hard-coding it in the `DocumentCodec`, the decision is 
 abstracted via the `BsonTypeClassMap` class.