webhook-walkthrough: Replace references to old-style fixture directories.
webhook-walkthrough: Replace references to old-style fixture directories.

The webhook walkthrough has now been updated to reflect the recent
decision to store webhook fixtures in
zerver/webhooks/<webhook_name>/fixtures/ as opposed to
zerver/fixtures/<webhook_name>/.

andersk/zulip,ryanbackman/zulip,timabbott/zulip,showell/zulip,andersk/zulip,synicalsyntax/zulip,rht/zulip,hackerkid/zulip,brainwane/zulip,showell/zulip,timabbott/zulip,ryanbackman/zulip,mahim97/zulip,Galexrt/zulip,jrowan/zulip,brainwane/zulip,verma-varsha/zulip,Galexrt/zulip,synicalsyntax/zulip,j831/zulip,rishig/zulip,rht/zulip,shubhamdhama/zulip,synicalsyntax/zulip,andersk/zulip,timabbott/zulip,showell/zulip,Galexrt/zulip,hackerkid/zulip,tommyip/zulip,christi3k/zulip,punchagan/zulip,hackerkid/zulip,jrowan/zulip,brockwhittaker/zulip,zulip/zulip,kou/zulip,zulip/zulip,synicalsyntax/zulip,shubhamdhama/zulip,punchagan/zulip,vaidap/zulip,zulip/zulip,ryanbackman/zulip,christi3k/zulip,eeshangarg/zulip,rht/zulip,brockwhittaker/zulip,jphilipsen05/zulip,vabs22/zulip,dhcrzf/zulip,eeshangarg/zulip,dhcrzf/zulip,jphilipsen05/zulip,timabbott/zulip,vabs22/zulip,jphilipsen05/zulip,rht/zulip,eeshangarg/zulip,shubhamdhama/zulip,timabbott/zulip,Galexrt/zulip,vabs22/zulip,tommyip/zulip,rht/zulip,Galexrt/zulip,rht/zulip,rishig/zulip,kou/zulip,hackerkid/zulip,kou/zulip,zulip/zulip,verma-varsha/zulip,eeshangarg/zulip,andersk/zulip,mahim97/zulip,j831/zulip,brainwane/zulip,punchagan/zulip,eeshangarg/zulip,jackrzhang/zulip,jackrzhang/zulip,verma-varsha/zulip,mahim97/zulip,synicalsyntax/zulip,zulip/zulip,brainwane/zulip,brainwane/zulip,vaidap/zulip,shubhamdhama/zulip,brainwane/zulip,kou/zulip,jphilipsen05/zulip,mahim97/zulip,kou/zulip,jphilipsen05/zulip,rishig/zulip,amanharitsh123/zulip,zulip/zulip,kou/zulip,rishig/zulip,j831/zulip,rishig/zulip,vaidap/zulip,christi3k/zulip,showell/zulip,vaidap/zulip,punchagan/zulip,jackrzhang/zulip,j831/zulip,vabs22/zulip,mahim97/zulip,dhcrzf/zulip,christi3k/zulip,tommyip/zulip,shubhamdhama/zulip,amanharitsh123/zulip,rishig/zulip,dhcrzf/zulip,amanharitsh123/zulip,brainwane/zulip,amanharitsh123/zulip,jrowan/zulip,vaidap/zulip,brockwhittaker/zulip,mahim97/zulip,tommyip/zulip,jackrzhang/zulip,andersk/zulip,showell/zulip,shubhamdhama/zulip,verma-varsha/zulip,brockwhittaker/zulip,amanharitsh123/zulip,ryanbackman/zulip,jackrzhang/zulip,rht/zulip,Galexrt/zulip,vaidap/zulip,timabbott/zulip,showell/zulip,dhcrzf/zulip,timabbott/zulip,punchagan/zulip,jrowan/zulip,showell/zulip,verma-varsha/zulip,tommyip/zulip,hackerkid/zulip,j831/zulip,hackerkid/zulip,vabs22/zulip,j831/zulip,jackrzhang/zulip,eeshangarg/zulip,brockwhittaker/zulip,kou/zulip,brockwhittaker/zulip,punchagan/zulip,punchagan/zulip,jphilipsen05/zulip,shubhamdhama/zulip,synicalsyntax/zulip,jackrzhang/zulip,tommyip/zulip,christi3k/zulip,andersk/zulip,dhcrzf/zulip,Galexrt/zulip,jrowan/zulip,verma-varsha/zulip,synicalsyntax/zulip,rishig/zulip,ryanbackman/zulip,dhcrzf/zulip,zulip/zulip,eeshangarg/zulip,ryanbackman/zulip,andersk/zulip,jrowan/zulip,tommyip/zulip,amanharitsh123/zulip,hackerkid/zulip,vabs22/zulip,christi3k/zulip