Update api.md
Fix timestamp in example in exemplars query. The year was `020` instead of `2020`.
@@ -361,7 +361,7 @@ URL query parameters:
- `end=<rfc3339 | unix_timestamp>`: End timestamp.
```json
-$ curl -g 'http://localhost:9090/api/v1/query_exemplars?query=test_exemplar_metric_total&start=2020-09-14T15:22:25.479Z&end=020-09-14T15:23:25.479Z'
+$ curl -g 'http://localhost:9090/api/v1/query_exemplars?query=test_exemplar_metric_total&start=2020-09-14T15:22:25.479Z&end=2020-09-14T15:23:25.479Z'
{
"status": "success",
"data": [
