Fix html report path

Author: asze17

book/src/user_guide/html_report.md

@@ -1,7 +1,7 @@
 # HTML Report
 
 Criterion.rs can generate an HTML report displaying the results of the benchmark under
-`target/criterion/report/index.html`. By default, the plots are generated using
+`target/criterion/reports/index.html`. By default, the plots are generated using
 [gnuplot](http://www.gnuplot.info/) if it is available, or the
 [plotters](https://github.com/38/plotters) crate if it is not. The example below was generated
 using the gnuplot backend, but the charts generated by plotters are similar.