Bump aws sdk to v1.15.11

This is the latest official release for this dependency

Signed-off-by: Ryan Abrams <rdabrams@gmail.com>

vendor/github.com/aws/aws-sdk-go/private/protocol/rest/build.go

@@ -20,9 +20,6 @@ import (
 	"github.com/aws/aws-sdk-go/private/protocol"
 )
 
-// RFC822 returns an RFC822 formatted timestamp for AWS protocols
-const RFC822 = "Mon, 2 Jan 2006 15:04:05 GMT"
-
 // Whether the byte value can be sent without escaping in AWS URLs
 var noEscape [256]bool
 
@@ -270,7 +267,14 @@ func convertType(v reflect.Value, tag reflect.StructTag) (str string, err error)
 	case float64:
 		str = strconv.FormatFloat(value, 'f', -1, 64)
 	case time.Time:
-		str = value.UTC().Format(RFC822)
+		format := tag.Get("timestampFormat")
+		if len(format) == 0 {
+			format = protocol.RFC822TimeFormatName
+			if tag.Get("location") == "querystring" {
+				format = protocol.ISO8601TimeFormatName
+			}
+		}
+		str = protocol.FormatTime(format, value)
 	case aws.JSONValue:
 		if len(value) == 0 {
 			return "", errValueNotSet