noise.sdf: add min="0.0" to the precision and dynamic_bias_correlation_time parameters

[osrf-migration]

Original report (archived issue) by Steve Peters (Bitbucket: Steven Peters, GitHub: scpeters).

---

This is a follow-up task from pr #329, which proposed to "Add random walk params to noise for sdf 1.6". Most of the changes in this PR have already been merged in PR #525 except for the differences noted in the following comment:

• https://osrf-migration.github.io/sdformat-gh-pages/#!/osrf/sdformat/pull-requests/329/add-random-walk-params-to-noise-for-sdf-16/diff#comment-134273497

Two of the differences are still worth applying, but I'm putting them in an issue to be resolved after the migration to GitHub.

• noise.sdf: add min="0.0" to the precision parameter
• noise.sdf: add min="0.0" to the dynamic_bias_correlation_time parameter

[osrf-migration]

Original comment by Steve Peters (Bitbucket: Steven Peters, GitHub: scpeters).

---

For reference, the changes from pr #329 have been pulled into this repo as 9b5a4bc.