pkg: Use node 10

Node 11 doesn't seem to be supported by pkg, also node 10 is an LTS
release, so we may as well use that.

vercel/pkg#584

package.json

@@ -5,7 +5,7 @@
   "main": "index.js",
   "scripts": {
     "build": "tsc",
-    "pkg": "pkg -o google-keep-exporter --targets 'linux,macos,win' dist/main.js",
+    "pkg": "pkg -o google-keep-exporter --targets 'node10-linux,node10-macos,node10-win' dist/main.js",
     "test": "jest src/**"
   },
   "author": "Vishesh Handa <me@vhanda.in>",