adjust DOCROOT_URL_SLASH to just be /

Testing the value of using:

```sh
DOCROOT_URL_SLASH="/"
```

in case doing "../../" isn't liked by GitHub.

bin/gen-author.sh

@@ -74,7 +74,7 @@ export PANDOC_WRAPPER="bin/pandoc_wrapper.sh"
 export PANDOC_WRAPPER_OPTSTR="-f markdown -t html --fail-if-warnings=true"
 export REPO_URL="https://github.com/ioccc-src/temp-test-ioccc"
 export TOP_URL="https://ioccc-src.github.io/temp-test-ioccc"
-export DOCROOT_URL_SLASH="../../"
+export DOCROOT_URL_SLASH="/"
 
 # set usage message
 #

bin/subst.winner-index.sh

@@ -111,7 +111,7 @@ $NAME version: $VERSION"
 #
 export NOOP=
 export DO_NOT_PROCESS=
-export DOCROOT_URL_SLASH="../../"
+export DOCROOT_URL_SLASH="/"
 
 # parse command line
 #