package.json: use ^ in versions

Author: feross

package.json

@@ -32,11 +32,11 @@
     "once": "^1.3.0",
     "run-series": "^1.0.2",
     "simple-get": "^1.3.0",
-    "simple-peer": "4.0.4",
-    "simple-websocket": "1.0.4",
+    "simple-peer": "^4.0.4",
+    "simple-websocket": "^1.0.4",
     "string2compact": "^1.1.1",
     "ws": "^0.7.1",
-    "xtend": "4.0.0"
+    "xtend": "^4.0.0"
   },
   "devDependencies": {
     "magnet-uri": "^4.0.0",