Use npm to install global dependencies

Author: Ruben Schmidmeister

.travis.yml

@@ -4,7 +4,7 @@ node_js:
 
 install:
 - yarn install
-- yarn add --global codecov istanbul
+- npm install --global codecov istanbul
 
 script:
 - yarn standard index.js

package.json

@@ -22,5 +22,8 @@
   "devDependencies": {
     "mocha": "^6.2.2",
     "standard": "^14.3.1"
+  },
+  "dependencies": {
+    "istanbul": "^0.4.5"
   }
 }