Update icon for generic attachments.

Signal/Images.xcassets/generic-attachment.imageset/Contents.json

@@ -2,17 +2,17 @@
   "images" : [
     {
       "idiom" : "universal",
-      "filename" : "File@1x.png",
+      "filename" : "file-light-large@1x.png",
       "scale" : "1x"
     },
     {
       "idiom" : "universal",
-      "filename" : "File@2x.png",
+      "filename" : "file-light-large@2x.png",
       "scale" : "2x"
     },
     {
       "idiom" : "universal",
-      "filename" : "File@3x.png",
+      "filename" : "file-light-large@3x.png",
       "scale" : "3x"
     }
   ],