修改文件保持和官方的文件一致

operations/alerts.md

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+---
+id: alerts
+title: "Alerts"
+---
+
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+
+
+Druid generates alerts on getting into unexpected situations.
+
+Alerts are emitted as JSON objects to a runtime log file or over HTTP (to a service such as Apache Kafka). Alert emission is disabled by default.
+
+All Druid alerts share a common set of fields:
+
+* `timestamp` - the time the alert was created
+* `service` - the service name that emitted the alert
+* `host` - the host name that emitted the alert
+* `severity` - severity of the alert e.g. anomaly, component-failure, service-failure etc.
+* `description` - a description of the alert
+* `data` - if there was an exception then a JSON object with fields `exceptionType`, `exceptionMessage` and `exceptionStackTrace`