Bump serde from 1.0.85 to 1.0.87

[dependabot-preview]

Bumps serde from 1.0.85 to 1.0.87.

Release notes

Sourced from serde's releases.

v1.0.87

• Fix inclusion of tag in struct containing flattened fields (#1468, thanks jwillbold)

v1.0.86

• Implement Serialize and Deserialize for core::ops::Bound<T> (#1466, thanks 0nkery)

Commits

• 134f268 Release 1.0.87
• c473633 Format with rustfmt 2018-12-10
• 6a3a820 Merge pull request #1474 from jwillbold/master
• 1d6ef76 Fixed #1468, flattened struct fields made structs ignore their tag
• c8e3959 Release 1.0.86
• 796f412 Document that Bound impls exist
• fa854a2 Format with rustfmt 2018-12-10
• 3a097ff Deserialize Bound::Unbounded as unit variant
• 8463bfc Remove as yet unrequested range impls
• 7a72b4c Merge pull request #1466 from 0nkery/master
• Additional commits viewable in compare view

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