Update Swagger Codegen to v1.5.15

[fehguy]

Fixes #5753

Updates swagger-core, swagger-parser to the latest production versions

[wing328]

@fehguy did some tests and found that there are changes to type: string, format: byte. Here is an example for the C# Petstore samples with fake endpoints.

@@ -149,7 +149,7 @@ namespace IO.Swagger.Model
         /// Gets or Sets _Byte
         /// </summary>
         [DataMember(Name="byte", EmitDefaultValue=false)]
-        public byte[] _Byte { get; set; }
+        public string _Byte { get; set; }

Other generators (e.g. PHP, Ruby, Python, etc) experience similar changes.

It seems like the format: byte is ignored, and here is the definition of the parameter:

        - name: byte
          type: string
          format: byte
          in: formData
          description: None
          required: true

[fehguy]

Thanks I'll look into this