small grammar change (reactjs#190)

jeanlange · timdorr · commit f4516e341a74 · 2016-06-29T17:26:12.000-04:00
diff --git a/lessons/10-clean-urls/README.md b/lessons/10-clean-urls/README.md
@@ -1,6 +1,6 @@
 # Clean URLs with Browser History
 
-The URLs in our app right now are built on a hack: the hash. Its the
+The URLs in our app right now are built on a hack: the hash. It's the
 default because it will always work, but there's a better way.
 
 Modern browsers let JavaScript manipulate the URL without making an http
