Build failure when using `void` in REST docs

```
1) Swagger API Declarations verify get api declarations:
     Uncaught AssertionError: ResponseClass type "void" is undefined in models
      at /home/travis/build/oaeproject/Hilary/node_modules/oae-util/tests/test-swagger.js:125:44
      at Array.forEach (native)
      at Function._.each._.forEach (/home/travis/build/oaeproject/Hilary/node_modules/underscore/underscore.js:79:11)
      at /home/travis/build/oaeproject/Hilary/node_modules/oae-util/tests/test-swagger.js:114:31
      at Array.forEach (native)
      at Function._.each._.forEach (/home/travis/build/oaeproject/Hilary/node_modules/underscore/underscore.js:79:11)
      at /home/travis/build/oaeproject/Hilary/node_modules/oae-util/tests/test-swagger.js:110:27
      at Request._callback (/home/travis/build/oaeproject/Hilary/node_modules/oae-rest/lib/util.js:9:8823)
      at Request.self.callback (/home/travis/build/oaeproject/Hilary/node_modules/oae-rest/node_modules/request/request.js:121:22)
      at Request.EventEmitter.emit (events.js:98:17)
```