Improper handling of BinaryMediaTypes property

[keetonian]

Description:

After doing additional verification work with the BinaryMediaTypes property and the fix implemented in #954, I found that the fix still contains an issue.

The BinaryMediaTypes property requires encoded values, so image/gif should be passed to this property as image~1gif.

The x-amazon-apigateway-binary-media-types swagger property cannot read the encoded value, and so the values should be passed to it as image/gif.

Steps to reproduce the issue:

1. Deploy an API with a binary media type in encoded format
2. Verify API deployed correctly
3. Deploy API again, updating BMT section with an additional media type
4. Verify that the new media type is deployed correctly, but the old type (sometimes) is switched from using a / to using the encoded value (~1) which is incorrect.

Fix: replace ~1 with / for x-amazon-apigateway-binary-media-types property.

[keetonian]

Patch fix: 1.13.1