change password placeholder image

pass/Assets.xcassets/PasswordImagePlaceHolder.imageset/Contents.json

@@ -6,12 +6,12 @@
     },
     {
       "idiom" : "universal",
-      "filename" : "padlock.pdf",
+      "filename" : "key.pdf",
       "scale" : "2x"
     },
     {
       "idiom" : "universal",
-      "filename" : "padlock-1.pdf",
+      "filename" : "key-1.pdf",
       "scale" : "3x"
     }
   ],