Update manifest with new icons

Author: Chrisvin

extension/manifest.json

@@ -6,17 +6,15 @@
     "description" : "Adds an 'so' omnibox command to search Stack Overflow.",
 
     "icons": {
-        "16": "icons/search_black_16.png",
-        "18": "icons/search_black_18dp.png",
-        "24": "icons/search_black_24dp.png",
-        "36": "icons/search_black_36dp.png",
-        "48": "icons/search_black_48dp.png"
+        "16": "icons/16.png",
+        "48": "icons/48.png",
+        "128": "icons/128.png"
     },
 
     "omnibox": { 
         "keyword" : "so",
         "icons": {
-            "16": "icons/search_black_16.png"
+            "16": "icons/16.png"
         }
     },