Explicitly install peerdependencies

Builds against recent nodejs versions are failing due to
missing peerdependencies. This adds the following packages
explicitly in package.json:

 * acorn
 * ajv

Fixes #1230 (properly)

package.json

@@ -1,6 +1,6 @@
 {
   "name": "fauxton",
-  "version": "1.2.1",
+  "version": "1.2.2",
   "description": "Fauxton is a modular CouchDB dashboard and Futon replacement.",
   "main": "./index.js",
   "directories": {
@@ -34,6 +34,8 @@
     "@babel/preset-react": "^7.0.0",
     "@babel/register": "^7.4.4",
     "@webcomponents/url": "~0.7.1",
+    "acorn": "^6.0.0",
+    "ajv": "^6.9.1",
     "async": "~0.2.6",
     "babel-eslint": "^9.0.0",
     "babel-loader": "^8.0.6",