Fix reference to BenchmarkBase.dart

Signed-off-by: John McCutchan <john@johnmccutchan.com>
diff --git a/lib/benchmark_harness.dart b/lib/benchmark_harness.dart
index 842b2b1..c921fa9 100644
--- a/lib/benchmark_harness.dart
+++ b/lib/benchmark_harness.dart
@@ -1,3 +1,3 @@
 library benchmark_harness;
 
-part 'src/BenchmarkBase.dart';
+part 'src/benchmark_base.dart';