FIx README v1.0.0 (#63)

## Problem
Missed completely removing the old `metadata` example in Query by
Vector. Nice catch @jseldess.

## Solution
Fix it.

## Type of Change
- [ ] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to not work as expected)
- [ ] This change requires a documentation update
- [ ] Infrastructure change (CI configs, etc)
- [X] Non-code change (docs, etc)
- [ ] None of the above: (explain here)

## Test Plan
N/A

README.md

@@ -639,12 +639,7 @@ func main() {
 		"year": 2019,
 	}
 
-	metadataFilter, err := structpb.NewStruct(map[string]interface{}{
-		"genre": map[string]interface{}{
-			"$eq": "documentary",
-		},
-		"year": 2019,
-	})
+	metadataFilter, err := structpb.NewStruct(metadataMap)
 	if err != nil {
 		log.Fatalf("Failed to create metadataFilter: %v", err)
 	}