fix copy and paste error

Author: Christian Pietsch

rest_api_koans.md

@@ -27,7 +27,7 @@ You might start by wondering how much and what kinds of data exist in the CrossR
 
 ### How many report DOIs does CrossRef have?
 
-    http://api.crossref.org/types/journal-article/works?rows=0
+    http://api.crossref.org/types/report/works?rows=0
 
 But eventually you will probably want to start looking at metadata records