Use `zap.Error` instead of `zap.String` for logging errors: change all expressions like
`zap.String("error", err.Error())` or `zap.String("err", err.Error())` to `zap.Error(err)`.
Leave similar expressions with other messages unchanged, for example,
`zap.String("last_error", lastErr.Error())` or `zap.String("reason", ctx.Err().Error())`.
This change was made by applying the following patch:
```diff
@@
var err expression
@@
-zap.String("error", err.Error())
+zap.Error(err)
@@
var err expression
@@
-zap.String("err", err.Error())
+zap.Error(err)
```
Signed-off-by: Aleksey Savchuk <a.savchuk@yadro.com>
