Small rewording in folly Benchmark comment

Summary: A bit more clear

Reviewed By: yfeldblum

Differential Revision: D4075931

fbshipit-source-id: 1398500336d412b5e7663ef1e67b20a329ce2979

folly/Benchmark.h

@@ -423,7 +423,7 @@ void doNotOptimizeAway(T&& datum) {
 /**
  * Just like BENCHMARK, but prints the time relative to a
  * baseline. The baseline is the most recent BENCHMARK() seen in
- * lexical order. Example:
+ * the current scope. Example:
  *
  * // This is the baseline
  * BENCHMARK(insertVectorBegin, n) {