change log level for BigQuery exception to WARN (#231)

Author: Yohei Onishi

kcbq-connector/src/main/java/com/wepay/kafka/connect/bigquery/write/batch/TableWriter.java

@@ -81,7 +81,7 @@ public void run() {
           currentIndex += currentBatchSize;
           successCount++;
         } catch (BigQueryException err) {
-          logger.debug("Could not write batch of size {} to BigQuery.", currentBatch.size(), err);
+          logger.warn("Could not write batch of size {} to BigQuery.", currentBatch.size(), err);
           if (isBatchSizeError(err)) {
             failureCount++;
             currentBatchSize = getNewBatchSize(currentBatchSize);