Fix a typo in the similarity docs (#26970)

agent5566 · rjernst · commit 1c3e02cea5d3 · 2017-10-12T09:27:49.000-07:00
diff --git a/docs/reference/index-modules/similarity.asciidoc b/docs/reference/index-modules/similarity.asciidoc
@@ -5,7 +5,7 @@ A similarity (scoring / ranking model) defines how matching documents
 are scored. Similarity is per field, meaning that via the mapping one
 can define a different similarity per field.
 
-Configuring a custom similarity is considered a expert feature and the
+Configuring a custom similarity is considered an expert feature and the
 builtin similarities are most likely sufficient as is described in
 <<similarity>>.
 
