ci: update travis config

.travis.yml

@@ -7,7 +7,7 @@ node_js:
 
 cache:
   directories:
-    - $HOME/.cache/yarn
+    - node_modules
 
 addons:
   apt:
@@ -16,12 +16,8 @@ addons:
     packages:
       - g++-4.8
 
-before_install:
-  - curl -o- -L https://yarnpkg.com/install.sh | bash
-  - export PATH=$HOME/.yarn/bin:$PATH
-
 install:
-  - yarn
+  - npm i
 
 script:
   - npm run build:ci