Updates to braintree_java

Afternoon, 

This pull request includes the following updates:

1. Added use of StringBuilder in place of += (a String is a immutable object)
2. Fixed security issue: Array is stored directly
   1 in Environment - Added Arrays.copyOf
   1 in Http - Added Arrays.copyOf
3. Commented out CardType.SWITCH as it no longer exists
4. String equality == used in ValidationErrors and NodeWrapper