Missing break in case in DBTestBase::CurrentOptions

Summary:
Found by gcc-7 compile error.

This appeared to be a fault as these options seems too different.
Closes https://github.com/facebook/rocksdb/pull/1667

Differential Revision: D4324174

Pulled By: yiwu-arbug

fbshipit-source-id: 0f65383

db/db_test_util.cc

@@ -307,6 +307,7 @@ Options DBTestBase::CurrentOptions(
       break;
     case kManifestFileSize:
       options.max_manifest_file_size = 50;  // 50 bytes
+      break;
     case kPerfOptions:
       options.soft_rate_limit = 2.0;
       options.delayed_write_rate = 8 * 1024 * 1024;