minor typo fix in mongodump

Author: monkey101

source/reference/mongodump.txt

@@ -128,7 +128,7 @@ Options
 
    Use the :option:`--collection` option to specify a collection for
    :program:`mongodump` to backup. If you do not specify a collection,
-   this options copies all collections in the specified database or
+   this option copies all collections in the specified database or
    instance to the dump files. Use this option to backup or copy a
    smaller subset of your data.