perf(GtfsValidationPlus): Close CSV reader after use.

src/main/java/com/conveyal/datatools/manager/gtfsplus/GtfsPlusValidation.java

@@ -167,6 +167,7 @@ private static void validateTable(
             }
             rowIndex++;
         }
+        csvReader.close();
 
         // Add issue for wrong number of columns after processing all rows.
         // Note: We considered adding an issue for each row, but opted for the single error approach because there's no