Update asv requirement from <0.6,>=0.5.1 to >=0.5.1,<0.7

Updates the requirements on [asv](https://github.com/airspeed-velocity/asv) to permit the latest version.
- [Release notes](https://github.com/airspeed-velocity/asv/releases)
- [Changelog](https://github.com/airspeed-velocity/asv/blob/master/CHANGES.rst)
- [Commits](airspeed-velocity/asv@v0.5.1...v0.6.0)

---
updated-dependencies:
- dependency-name: asv
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

benchmarks/requirements.txt

@@ -1,3 +1,3 @@
 # Dependencies needed to run the benchmarks
 virtualenv
-asv>=0.5.1,<0.6
+asv>=0.5.1,<0.7