fix(logging): update the API

#### logging:v2
The following keys were changed:
- schemas.MetricDescriptor.description

discovery/logging-v2.json

@@ -3222,7 +3222,7 @@
       }
     }
   },
-  "revision": "20200624",
+  "revision": "20200724",
   "rootUrl": "https://logging.googleapis.com/",
   "schemas": {
     "BigQueryOptions": {
@@ -4008,7 +4008,7 @@
       "type": "object"
     },
     "MetricDescriptor": {
-      "description": "Defines a metric type and its schema. Once a metric descriptor is created, deleting or altering it stops data collection and makes the metric type's existing data unusable.The following are specific rules for service defined Monitoring metric descriptors:\ntype, metric_kind, value_type, description, display_name,  launch_stage fields are all required. The unit field must be specified  if the value_type is any of DOUBLE, INT64, DISTRIBUTION.\nMaximum of default 500 metric descriptors per service is allowed.\nMaximum of default 10 labels per metric descriptor is allowed.The default maximum limit can be overridden. Please follow https://cloud.google.com/monitoring/quotas",
+      "description": "Defines a metric type and its schema. Once a metric descriptor is created, deleting or altering it stops data collection and makes the metric type's existing data unusable.The following are specific rules for service defined Monitoring metric descriptors:\ntype, metric_kind, value_type and description  fields are all required. The unit field must be specified  if the value_type is any of DOUBLE, INT64, DISTRIBUTION.\nMaximum of default 500 metric descriptors per service is allowed.\nMaximum of default 10 labels per metric descriptor is allowed.The default maximum limit can be overridden. Please follow https://cloud.google.com/monitoring/quotas",
       "id": "MetricDescriptor",
       "properties": {
         "description": {

src/apis/logging/v2.ts

@@ -730,7 +730,7 @@ export namespace logging_v2 {
     writerIdentity?: string | null;
   }
   /**
-   * Defines a metric type and its schema. Once a metric descriptor is created, deleting or altering it stops data collection and makes the metric type's existing data unusable.The following are specific rules for service defined Monitoring metric descriptors: type, metric_kind, value_type, description, display_name,  launch_stage fields are all required. The unit field must be specified  if the value_type is any of DOUBLE, INT64, DISTRIBUTION. Maximum of default 500 metric descriptors per service is allowed. Maximum of default 10 labels per metric descriptor is allowed.The default maximum limit can be overridden. Please follow https://cloud.google.com/monitoring/quotas
+   * Defines a metric type and its schema. Once a metric descriptor is created, deleting or altering it stops data collection and makes the metric type's existing data unusable.The following are specific rules for service defined Monitoring metric descriptors: type, metric_kind, value_type and description  fields are all required. The unit field must be specified  if the value_type is any of DOUBLE, INT64, DISTRIBUTION. Maximum of default 500 metric descriptors per service is allowed. Maximum of default 10 labels per metric descriptor is allowed.The default maximum limit can be overridden. Please follow https://cloud.google.com/monitoring/quotas
    */
   export interface Schema$MetricDescriptor {
     /**