Merge pull request #28 from chain4travel/zip_code_correction

zipcode corrected to string

proto/cmp/types/v1alpha/address.proto

@@ -12,6 +12,6 @@ message Address {
   string line_1 = 1;
   string line_2 = 2;
   string district = 3;
-  int32 zip_code = 5;
+  string zip_code = 5;
   GeoTree geo_tree = 6;
 }