Update prometheus requirement from 0.7.0 to 0.8.0

[dependabot-preview]

Updates the requirements on prometheus to permit the latest version.

Changelog

Sourced from prometheus's changelog.

0.8.0

• Add: Reset Counters (#261)

• Add: Discard Histogram timers (#257)

• Add: observe_closure_duration for better observing closure duration for local histogram (#296)

• Fix a bug that global labels are not handled correctly (#269)

• Improve linear bucket accuracy by avoiding accumulating error (#276)

• Internal change: Use thiserror to generate the error structure (#285)

• Internal change: Switch from procinfo to procfs (#290)

• Internal change: Update to newer dependencies

0.7.0

• Provide immutable interface for local counters.

0.6.1

• Fix compile error when ProtoBuf feature is not enabled (#240).

0.6.0

• Add: Expose the default registry (#231).

• Add: Support common namespace prefix and common labels (#233).

0.5.0

• Change: Added TLS and BasicAuthentication support to push client.

0.4.2

• Change: Update to use protobuf 2.0.

0.4.1

• Change: (Local)(Int)Counter.inc_by only panics in debug build if the given value is < 0 (#168).

0.4.0

• Add: Provides IntCounter, IntCounterVec, IntGauge, IntGaugeVec, LocalIntCounter, LocalIntCounterVec for better performance when metric values are all integers (#158).

• Change: When the given value is < 0, (Local)Counter.inc_by no longer return errors, instead it will panic (#156).

... (truncated)

Commits

• 2cab356 Bump 0.8.0 (#309)
• 767b28c Update to reqwest 0.10 (#307)
• d919ccd Add LocalMetric trait (#297)
• e48cdac add method observe_closure_duration (#296)
• 6949f4d Update copyright header (#295)
• 3e2e928 Switch from procinfo to procfs (#290)
• 404f38a accept 200 response code when pushing to pushgateway (#288)
• f9f76b7 Use thiserror instead of quick-error (#285)
• 6aba569 Update syn, quote, proc-macro2 to v1.0 (#289)
• b668f39 Add accessor for histogram (#286)
• Additional commits viewable in compare view

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[dependabot-preview]

Looks like prometheus is up-to-date now, so this is no longer needed.