Fix stray partial link in 2019/dogon/README.md

This was at the top of the file on the same line as '## To build:' and
it caused strange output in the index.html file (and was incorrect in
any case).

2019/dogon/README.md

@@ -1,4 +1,4 @@
-%%REPO_URL%%/2019/lynn/## To build:
+## To build:
 
 ``` <!---sh-->
     make