chore(app): use relative urls so testing and preview are live

public/assets/phosphor-icons.sketchplugin/Contents/Sketch/manifest.json

@@ -0,0 +1,33 @@
+{
+  "compatibleVersion": 3,
+  "bundleVersion": 1,
+  "commands": [
+    {
+      "name": "Icon Palette",
+      "identifier": "phosphor-icons.icon-palette-identifier",
+      "script": "__icon-palette.js",
+      "shortcut": "cmd shift i",
+      "handlers": {
+        "run": "onRun",
+        "actions": {
+          "Shutdown": "onShutdown"
+        }
+      }
+    }
+  ],
+  "menu": {
+    "title": "Phosphor Icons",
+    "items": [
+      "phosphor-icons.icon-palette-identifier"
+    ]
+  },
+  "version": "2.1.4",
+  "description": "A flexible icon family for interfaces, diagrams, presentations — whatever, really.",
+  "homepage": "https://phosphoricons.com",
+  "name": "Phosphor Icons",
+  "identifier": "Phosphor Icons",
+  "disableCocoaScriptPreprocessor": true,
+  "appcast": "https://raw.githubusercontent.com/phosphor-icons/sketch/master/.appcast.xml",
+  "author": "Tobias Fried",
+  "authorEmail": "friedtm@gmail.com"
+}