fix url to testing buildpack

bin/test

@@ -2,7 +2,7 @@
 
 #
 # Create a Heroku app with the following buildpack:
-# https://github.com/ddollar/buildpack-tet
+# https://github.com/ddollar/buildpack-test
 #
 # Push this Python buildpack to that Heroku app to
 # run the tests.