docs(samples): fix sample issue (#1086)

Fixes b/177938551

Author: stephaniewang526

samples/snippets/src/main/java/com/example/bigquery/ExtractTableToJson.java

@@ -43,7 +43,7 @@ public static void main(String[] args) {
 
     // Note that FormatOptions.json().toString() is not "JSON" but "NEWLINE_DELIMITED_JSON"
     // Using FormatOptions Enum for this will prevent problems with unexpected format names.
-    String dataFormat = FormatOptions.json().toString();
+    String dataFormat = FormatOptions.json().getType();
 
     extractTableToJson(projectId, datasetName, tableName, destinationUri, dataFormat);
   }

samples/snippets/src/test/java/com/example/bigquery/ExtractTableToJsonIT.java

@@ -72,7 +72,7 @@ public void testExtractTableToJson() {
     String tableName = "shakespeare";
     String destinationUri = "gs://" + GCS_BUCKET + "/extractTest.json";
     // FormatOptions.json() is not "JSON" but "NEWLINE_DELIMITED_JSON"
-    String dataFormat = FormatOptions.json().toString();
+    String dataFormat = FormatOptions.json().getType();
 
     // Extract table content to GCS in JSON format
     ExtractTableToJson.extractTableToJson(