[major] Move racer to peer dependency (#26)

* Move racer to peer dependency; add next version betas to versions

* 5.0.0-beta.1

* Pin enhanced-resolve and webpack versions (#28)

* 5.0.0-beta.2

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@derbyjs/derby-webpack",
-  "version": "4.0.2",
+  "version": "5.0.0-beta.2",
   "description": "Webpack based builder for Derby apps",
   "repository": {
     "type": "git",
@@ -25,7 +25,6 @@
     "os-browserify": "^0.3.0",
     "path-browserify": "^1.0.1",
     "process": "^0.11.10",
-    "racer": "^1.0.3",
     "stream-browserify": "^3.0.0",
     "stream-http": "^3.2.0",
     "url": "^0.11.0",
@@ -38,6 +37,7 @@
     "webpack-virtual-modules": "^0.5.0"
   },
   "peerDependencies": {
-    "derby": "^3.0.0"
+    "derby": "^3.0.0 || ^4.0.0-beta.1",
+    "racer": "^1.0.0 || ^2.0.0-beta.5"
   }
 }