Creating a wallet with a monthly allowance > $5 causes Brave to crash

[alexwykoff]

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

Describe the issue you encountered:
On a clean install, if a user selects a value other than the default of $5 when they create the wallet, Brave crashes.

Expected behavior:
The wallet should be created without issue.

• Platform (Win7, 8, 10? macOS? Linux distro?):
  Tested on OS X
• Brave Version:
  0.11.6, 0.12.0 RC1
• Steps to reproduce:
  1. Make sure to move your ~/Library/Application Support/brave folder out of the way or use a clean VM.
  2. Open Brave (version 0.11.6 or higher).
  3. Go to Preferences -> Payments.
  4. Select a value other than $5 in the drop-down.
  5. Attempt to create a wallet.
• Screenshot if needed:
  
• Any related issues:

[alexwykoff]

cc @bbondy @mrose17 @diracdeltas