No need for -- when calling yarn

Message from Travis output:
> warning From Yarn 1.0 onwards, scripts don't require "--" for options
> to be forwarded. In a future version, any explicit "--" will be
> forwarded as-is to the scripts.

.travis.yml

@@ -9,7 +9,7 @@ env:
 install:
 - yarn install --frozen-lockfile
 after_failure:
-- yarn build -- --inspect
+- yarn build --inspect
 script:
 - yarn build
 - yarn test