fix minor typo (#196)

Author: alexander-winkler

1.0-draft/index.html

@@ -170,7 +170,7 @@ <h3>History of the Reconciliation API</h3>
         <p>
           This API was originally designed by Metaweb as a protocol used between Freebase and Gridworks (now known as OpenRefine).
 	  Freebase was a free crowdsourced knowledge graph, storing data about a broad range of topics and exposed on the web as linked data.
-	  OpenRefine is tool which was originally designed to help populate this knowledge graph by importing data into it.
+	  OpenRefine is a tool which was originally designed to help populate this knowledge graph by importing data into it.
 	  It supports a range of operations which help the user reshape their data to prepare it for ingestion in a data model such as Freebase's.
 	  One of these operations is <emph>reconciliation</emph>, which matches mentions of entities in the local dataset to records in the target database. The reconciliation API was initially introduced to specify how OpenRefine and Freebase could communicate during that process. 
         </p>