set StripPrefix default to 1

Author: liufangtao

spring-cloud-gateway-server/src/main/java/org/springframework/cloud/gateway/filter/factory/StripPrefixGatewayFilterFactory.java

@@ -83,7 +83,10 @@ public String toString() {
 
 	public static class Config {
 
-		private int parts;
+		/**
+		 * set default value to 1
+		 */
+		private int parts = 1;
 
 		public int getParts() {
 			return parts;