configure wercker pipeline

* use npm-install wercker command

wercker.yml

@@ -11,7 +11,7 @@ test:
       name: install dependencies
       code: |
         yarn global add npm@4
-        npm install
+        npm-install
 
     - script:
       name: print dependencies
@@ -35,7 +35,7 @@ build-prod:
       name: install dependencies
       code: |
         yarn global add npm@4
-        npm install
+        npm-install
 
     - script:
       name: print dependencies