Add placeholder package version

We are using [semantic release](https://github.com/semantic-release/semantic-release)
to manage our NPM releases, but it's still important to have some sort
of version in the file at all times.

package.json

@@ -1,5 +1,6 @@
 {
   "name": "pelias-api",
+  "version": "0.0.0-semantic-release",
   "author": "mapzen",
   "description": "Pelias API",
   "homepage": "https://github.com/pelias/api",