Swagger file not included in generated static documentation

**Operating System**: (`Windows` or `Linux` or `MacOS`)

Windows

**DocFX Version Used**:

Latest NuGet

**Template used**: (`default` or `statictoc` or contain custom template)

statictoc

**Steps to Reproduce**:

1. Install NuGet package into WebAPI 2.0 solution
2. Add "contacts.swagger.json" (example from public DocFX website, unchanged) to "api" folder
3. Add "api/*.swagger.json" to "build"/"content"/"files"

**Expected Behavior**:

Open __site/api/index.html, Contacts should be in the left menu sidebar

**Actual Behavior**:

It is not.