[net] Fix use of definition lists in Markdown documentation.

Gitiles has moved to CommonMark and won't support definition lists. See
https://code.google.com/p/gitiles/issues/detail?id=89

[email protected]
BUG=none

Review-Url: https://codereview.chromium.org/2063843003
Cr-Commit-Position: refs/heads/master@{#399517}
1 file changed