fix filename in oneliners.md

docs/oneliners.md

 # Extracting group information with one liners
 
-This document lists a few one liners to extract useful group information from the JSON output of `collect_forks.json`.
+This document lists a few one liners to extract useful group information from the JSON output of `collect_forks.py`.
 
 * Find the number of groups
 ```sh
@@ -45,4 +45,4 @@ jq '.[] | .members | map(.name) | .[]' forks.json \
   | sed 's/^ *//' \
   | comm -23 <( sort enrolled_students.txt) -
 "John Smith"
-```
\ No newline at end of file
+```