Bug: Change margin for Expense Cards so they can fit two to a row in emulator

**Date Seen**
6/16/22

**Versions**
Android Emulator
Develop Branch

**Bug Description**
The Expense Cards are one to a row in the emulator, instead of 2 to a row as in the figma.

**Steps to Reproduce**

1. Start the app in emulator
2. Login
3. Add two expense cards
4. Note that the cards are stacked on top of each other instead of side by side

**Actual Behavior**
The expense cards appear in the Expense List in the emulator one per row instead of two per row.

**Expected Behavior**
The Expense Cards should be able to fit two per row in the emulator.

**Troubleshooting/Testing Steps Attempted**
The gap between them in the Figma appears to be 16. The margin in the container style for `ExpenseCard.tsx` is set to 15. If the margin is set to 8, then there will be 16 between the two cards and they should fit in a row of two in the emulator.

Note: It may be necessary to find a better long-term solution to make the Expense Cards properly responsive in smaller screens.