Update webhooks.rst
Update webhooks.rst

- missing colon
- the path to the attribute in the JSON object was incorrect
Plexxi/st2,pixelrebel/st2,dennybaa/st2,tonybaloney/st2,lakshmi-kannan/st2,tonybaloney/st2,StackStorm/st2,nzlosh/st2,Plexxi/st2,nzlosh/st2,punalpatel/st2,alfasin/st2,dennybaa/st2,Plexxi/st2,armab/st2,emedvedev/st2,emedvedev/st2,armab/st2,peak6/st2,punalpatel/st2,tonybaloney/st2,dennybaa/st2,armab/st2,lakshmi-kannan/st2,Plexxi/st2,emedvedev/st2,alfasin/st2,lakshmi-kannan/st2,nzlosh/st2,peak6/st2,punalpatel/st2,pixelrebel/st2,pixelrebel/st2,nzlosh/st2,peak6/st2,StackStorm/st2,alfasin/st2,StackStorm/st2,StackStorm/st2