adding dashes to yarn run commands to pass extra args

Author: Jake Goldsborough

package.json

@@ -9,9 +9,9 @@
   "scripts": {
     "build": "yarn run ember build",
     "start": "yarn run ember server",
-    "start:local": "yarn run ember server --proxy http://127.0.0.1:8888",
-    "start:staging": "yarn run ember server --proxy https://staging-crates-io.herokuapp.com",
-    "start:live": "yarn run ember server --proxy https://crates.io",
+    "start:local": "yarn run ember server -- --proxy http://127.0.0.1:8888",
+    "start:staging": "yarn run ember server -- --proxy https://staging-crates-io.herokuapp.com",
+    "start:live": "yarn run ember server -- --proxy https://crates.io",
     "test": "yarn run ember test",
     "ember": "ember"
   },