Make [wercker] no builds terminology consistent with other badges (#2957)

This makes the "no builds" state pass `isBuildStatus`, which is what fixes the failing tests:

https://circleci.com/gh/badges/daily-tests/138

services/wercker/wercker.service.js

@@ -57,7 +57,7 @@ module.exports = class Wercker extends BaseJsonService {
     })
     if (json.length === 0) {
       return this.constructor.render({
-        result: 'no builds',
+        result: 'not built',
       })
     }
     const { result } = json[0]

services/wercker/wercker.tester.js

@@ -58,4 +58,4 @@ t.create('CI status by ID (no runs yet)')
       .get('/runs?applicationId=559e33c8e982fc615500b357&limit=1')
       .reply(200, [])
   )
-  .expectJSON({ name: 'build', value: 'no builds' })
+  .expectJSON({ name: 'build', value: 'not built' })