This fix enables goimports check and fixes several imports format
so that the import sections are prettier, e.g.:
```
 import (
-       "github.com/miekg/dns"
        "regexp"
        "strconv"
        "strings"
+
+       "github.com/miekg/dns"
 )
```
Signed-off-by: Yong Tang <yong.tang.github@outlook.com>