CHANGELOG.md in benchmark_driver-0.15.7 vs CHANGELOG.md in benchmark_driver-0.15.8

@@ -1,4 +1,8 @@
+# v0.15.8
+
+- Add `--rvm` option and `.rvm` Ruby interface to use RVM
+
 # v0.15.7
 
 - Add `median` to --repeat-result options
 
 # v0.15.6