Update netlify.toml

Change deploy preview branch back to `main`

Author: phryneas

netlify.toml

@@ -13,7 +13,7 @@
   npm run docmodel
   cd ../
   rm -rf monodocs
-  git clone https://github.com/apollographql/docs --branch pr/expose-hook --single-branch monodocs
+  git clone https://github.com/apollographql/docs --branch main --single-branch monodocs
   cd monodocs
   npm i
   cp -r ../docs local