Update normalizers.asciidoc

analyzers -> normalizers

Author: clintongormley

docs/reference/analysis/normalizers.asciidoc

@@ -11,7 +11,7 @@ allowed, but not a stemming filter, which needs to look at the keyword as a
 whole.
 
 [float]
-=== Custom analyzers
+=== Custom normalizers
 
 Elasticsearch does not ship with built-in normalizers so far, so the only way
 to get one is by building a custom one. Custom normalizers take a list of char