Update 03b_github_collaboration.md

Git-Github/lessons/03b_github_collaboration.md

@@ -129,11 +129,12 @@ $ git push origin master
 ~~~
 ~~~ {.output}
 To https://github.com/vlad/planets.git
- ! [rejected]        master -> master (non-fast-forward)
-error: failed to push some refs to 'https://github.com/vlad/planets.git'
-hint: Updates were rejected because the tip of your current branch is behind
-hint: its remote counterpart. Merge the remote changes (e.g. 'git pull')
-hint: before pushing again.
+ ! [rejected]        master -> master (fetch first)
+error: failed to push some refs to 'github.com:vlad/planets.git'
+hint: Updates were rejected because the remote contains work that you do
+hint: not have locally. This is usually caused by another repository pushing
+hint: to the same ref. You may want to first integrate the remote changes
+hint: (e.g., 'git pull ...') before pushing again.
 hint: See the 'Note about fast-forwards' in 'git push --help' for details.
 ~~~