SCB-1351 Some issues about using toolkit plugin

fix bug about generating contract file

Signed-off-by: MabinGo <bin.ma@huawei.com>
diff --git a/common/src/main/java/org/apache/servicecomb/toolkit/common/DefaultContractsGenerator.java b/common/src/main/java/org/apache/servicecomb/toolkit/common/DefaultContractsGenerator.java
index 590020f..d3f5973 100755
--- a/common/src/main/java/org/apache/servicecomb/toolkit/common/DefaultContractsGenerator.java
+++ b/common/src/main/java/org/apache/servicecomb/toolkit/common/DefaultContractsGenerator.java
@@ -50,7 +50,7 @@
 
   private String outputDir = ".";
 
-  private String format = "yaml";
+  private String format = ".yaml";
 
   @Override
   public boolean canProcess(String type) {