fix(ci): aegir: not found

For some reason non-master/release branch build failed to find aegir on PATH.
This uses npx to ensure it always works

License: MIT
Signed-off-by: Marcin Rataj <lidel@lidel.org>

.travis.yml

@@ -45,7 +45,7 @@ jobs:
       script:
         - npx aegir build --bundlesize
         - npx aegir dep-check -- -i wrtc -i electron-webrtc
-        - npm run lint
+        - npx aegir lint
 
     - stage: test
       name: chrome