contrib/asv.conf.json

bisect: use standard one-line commit summary

This makes bisect use the standardized support for one-line commit
summary I added a while back. That means that it will respect the
`command-templates.oneline-summary` config. If also means that the
default output now includes the first line of the commit message (see
test impact).

Differential Revision: https://phab.mercurial-scm.org/D10245

{
    "version": 1,
    "project": "mercurial",
    "project_url": "https://mercurial-scm.org/",
    "repo": "..",
    "branches": ["default", "stable"],
    "environment_type": "virtualenv",
    "show_commit_url": "https://www.mercurial-scm.org/repo/hg/rev/",
    "benchmark_dir": "benchmarks",
    "env_dir": "../.asv/env",
    "results_dir": "../.asv/results",
    "html_dir": "../.asv/html"
}