build(package.json): force use yarn (#181)

Adds preinstall npm script that will encourage installing dependencies using yarn

closes #36

package.json

@@ -5,6 +5,7 @@
     "packages/*"
   ],
   "scripts": {
+    "preinstall": "scripts/preinstall-script.js",
     "precommit": "lint-staged",
     "commit": "git-cz",
     "test": "jest --coverage",
@@ -51,5 +52,6 @@
       "standard",
       "jest --bail --findRelatedTests"
     ]
-  }
+  },
+  "dependencies": {}
 }

scripts/preinstall-script.js

@@ -0,0 +1,24 @@
+#!/usr/bin/env node
+
+const setup =
+  '\nhttps://github.com/ViacomInc/data-point/blob/master/CONTRIBUTING.md#setup\n'
+
+if (process.env.npm_execpath.indexOf('yarn') === -1) {
+  console.error(
+    '\x1b[41m',
+    'Error: You must use yarn to install dependencies.\n\n',
+    'For help setting up this project please vist:',
+    '\x1b[0m',
+    '\x1b[36m',
+    '\n',
+    setup
+  )
+  process.exit(1)
+}
+
+console.warn(
+  '\x1b[36m%s\x1b[0m',
+  '\nWe recommend using yarn for this project instead of npm.\n' +
+    '\nTo learn more about why we use yarn visit:\n' +
+    setup
+)