PasswordInput: Add 8px margin between password input and show/hide button

The touchable-feedback area was right up against the right edge of
the password input. Give some margin in between, for some breathing
room.

Author: chrisbobbe

src/common/PasswordInput.js

@@ -12,6 +12,7 @@ import Touchable from './Touchable';
 const styles = createStyleSheet({
   showPasswordButton: {
     justifyContent: 'center',
+    marginLeft: 8,
   },
   showPasswordButtonIcon: {
     margin: 8,