hypsrc-test: Fix reference file path in cabal file

It appears the haddock insists on prefixing --hyperlinked-sourcer output
with directory which the source appeared in.

haddock.cabal

@@ -30,7 +30,7 @@ extra-source-files:
   html-test/src/*.hs
   html-test/ref/*.html
   hypsrc-test/src/*.hs
-  hypsrc-test/ref/*.html
+  hypsrc-test/ref/src/*.html
   latex-test/src/Simple/*.hs
   latex-test/ref/Simple/*.tex
   latex-test/ref/Simple/*.sty