Preferences : Payments : monthly budget dropdown is missing units

[alexwykoff]

Did you search for similar issues before submitting this one?
Yes

Describe the issue you encountered:
When opening the Payments preference pane, the monthly budget dropdown does not display units. This makes the amount ambiguous. Will it be 5 BTC or USD?

Expected behavior:
A unit should be displayed either on or next to the dropdown.

• Platform (Win7, 8, 10? macOS? Linux distro?):
  OS X
• Brave Version:
  0.11.6 (6d9ba0c)
• Steps to reproduce:
  1. Open Preferences
  2. Select Payments
  3. Open the Monthly Budget Dropdown
• Screenshot if needed:
  
• Any related issues:

[alexwykoff]

cc: @diracdeltas