Update shrink-index.asciidoc

Fix half-finished sentence

docs/reference/indices/shrink-index.asciidoc

@@ -76,8 +76,8 @@ Indices can only be shrunk if they satisfy the following requirements:
 * The index must have more primary shards than the target index.
 
 * The number of primary shards in the target index must be a factor of the
-  number of primary shards in the source index. must have more primary shards
-   than the target index.
+  number of primary shards in the source index. The source index must have
+  more primary shards than the target index.
 
 * The index must not contain more than `2,147,483,519` documents in total
   across all shards that will be shrunk into a single shard on the target index