Update buildpacks.md to reflect change in schema
change YAML example in buildpack docs from `buildpacks:` to `buildpack:`
@@ -65,7 +65,7 @@ Any paths in `Ignore` will be ignored by the skaffold file watcher, even if they
`Ignore` will only work in conjunction with `Paths`, and with none of the other custom artifact dependency types.
```yaml
-buildpacks:
+buildpack:
builder: "gcr.io/buildpacks/builder:v1"
dependencies:
paths:
