dynamically update the "serve" version for static deployments (#513)

Since we use Greenkeeper to update dependencies for `now-cli`,
we can depend on it to keep the version of `serve` that we use
for static deployments up-to-date at all times.

lib/read-metadata.js

@@ -6,13 +6,16 @@ const chalk = require('chalk')
 const { readFile } = require('fs-promise')
 const { parse: parseDockerfile } = require('docker-file-parser')
 
+// Ours
+const { devDependencies: { serve: serveVersion } } = require('../lib/pkg')
+
 // `package.json` used for "static" deployments
 const staticPackage = Object.freeze({
   scripts: {
     start: `NODE_ENV='production' serve ./content`
   },
   dependencies: {
-    serve: '5.1.4'
+    serve: serveVersion
   }
 })
 

package.json

@@ -107,6 +107,7 @@
     "lint-staged": "3.4.1",
     "pkg": "3.0.3",
     "prettier": "1.3.0",
+    "serve": "5.1.4",
     "slackup": "2.0.1",
     "xo": "0.18.1"
   }