Update module github.com/gophercloud/gophercloud to v0.18.0

[renovate[bot]]

This PR contains the following updates:

Package	Type	Update	Change
github.com/gophercloud/gophercloud	require	minor	v0.17.0 -> v0.18.0

---

Release Notes

gophercloud/gophercloud

### [`v0.18.0`](https://togithub.com/gophercloud/gophercloud/compare/v0.17.0...v0.18.0) [Compare Source](https://togithub.com/gophercloud/gophercloud/compare/v0.17.0...v0.18.0)

---

Configuration

📅 Schedule: At any time (no schedule defined).

🚦 Automerge: Enabled.

♻ Rebasing: Whenever PR becomes conflicted, or you tick the rebase/retry checkbox.

🔕 Ignore: Close this PR and you won't be reminded about this update again.

---

• [ ] If you want to rebase/retry this PR, check this box.

---

This PR has been generated by WhiteSource Renovate. View repository job log here.

[coveralls]

Pull Request Test Coverage Report for Build 928982050

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 86.594%

---

Totals
Change from base Build 871746829:	0.0%
Covered Lines:	239
Relevant Lines:	276

---

💛 - Coveralls