fix typo in bibtex

CITATION.bib

@@ -1,7 +1,7 @@
 @misc{tuningplaybookgithub,
   author = {Varun Godbole and George E. Dahl and Justin Gilmer and Christopher J. Shallue and Zachary Nado},
   title = {Deep Learning Tuning Playbook},
-  url = {http://github.com/google/tuning_playbook},
+  url = {https://github.com/google-research/tuning_playbook},
   year = {2023},
   note = "Version 1"
 }