Bump syn from 1.0.17 to 1.0.21

[dependabot-preview[bot]]

Bumps syn from 1.0.17 to 1.0.21.

Release notes

Sourced from syn's releases.

1.0.21

• Documentation improvements

1.0.20

• Improve span of error message when an error during syn::Macro::parse_body is triggered past the last token of the macro body (#791)

1.0.19

• Parse a more lenient extern type syntax inside extern blocks (#763)

1.0.18

• Ignore unparsed empty None-delimited groups at the end of a macro input (#783)

Commits

• f6c814a Release 1.0.21
• c504fbe Add crosslink icons to readme and rustdoc
• 80c0238 Release 1.0.20
• 5e65424 Merge pull request #791 from dtolnay/close
• 1451738 Somewhat better scope span for Macro::parse_body
• 89a9ab1 Update test suite to nightly-2020-05-10
• e51bb8b Release 1.0.19
• 8e016b4 Merge pull request #790 from dtolnay/ety
• e98f372 Parse ForeignItem type with generics and bounds
• f104279 Remove travis bug workaround
• Additional commits viewable in compare view

Dependabot will resolve any conflicts with this PR as long as you don't alter it yourself. You can also trigger a rebase manually by commenting @dependabot rebase.

---

Dependabot commands and options

You can trigger Dependabot actions by commenting on this PR: - `@dependabot rebase` will rebase this PR - `@dependabot recreate` will recreate this PR, overwriting any edits that have been made to it - `@dependabot merge` will merge this PR after your CI passes on it - `@dependabot squash and merge` will squash and merge this PR after your CI passes on it - `@dependabot cancel merge` will cancel a previously requested merge and block automerging - `@dependabot reopen` will reopen this PR if it is closed - `@dependabot close` will close this PR and stop Dependabot recreating it. You can achieve the same result by closing it manually - `@dependabot ignore this major version` will close this PR and stop Dependabot creating any more for this major version (unless you reopen the PR or upgrade to it yourself) - `@dependabot ignore this minor version` will close this PR and stop Dependabot creating any more for this minor version (unless you reopen the PR or upgrade to it yourself) - `@dependabot ignore this dependency` will close this PR and stop Dependabot creating any more for this dependency (unless you reopen the PR or upgrade to it yourself) - `@dependabot use these labels` will set the current labels as the default for future PRs for this repo and language - `@dependabot use these reviewers` will set the current reviewers as the default for future PRs for this repo and language - `@dependabot use these assignees` will set the current assignees as the default for future PRs for this repo and language - `@dependabot use this milestone` will set the current milestone as the default for future PRs for this repo and language - `@dependabot badge me` will comment on this PR with code to add a "Dependabot enabled" badge to your readme Additionally, you can set the following in your Dependabot [dashboard](https://app.dependabot.com): - Update frequency (including time of day and day of week) - Pull request limits (per update run and/or open at any time) - Out-of-range updates (receive only lockfile updates, if desired) - Security updates (receive only security updates, if desired)

[dependabot-preview[bot]]

OK, I won't notify you again about this release, but will get in touch when a new version is available. If you'd rather skip all updates until the next major or minor version, let me know by commenting @dependabot ignore this major version or @dependabot ignore this minor version.

If you change your mind, just re-open this PR and I'll resolve any conflicts on it.