Update Proguard rules to remove BouncyCastle class

Summary
`X509LDAPCertStoreSpi` uses a J2SE package that isn't available in
Android. This class isn't needed for 3DS2, so don't keep it in Proguard
rules.

Motivation
Fixes #2268

Testing
Ran lint and manually verified

stripe/proguard-rules.txt

@@ -5,6 +5,7 @@
 # Rules for BouncyCastle
 -keep class org.bouncycastle.jcajce.provider.** { *; }
 -keep class org.bouncycastle.jce.provider.** { *; }
+-keep class !org.bouncycastle.jce.provider.X509LDAPCertStoreSpi { *; }
 
 -keep class com.stripe.android.** { *; }
 -dontwarn com.stripe.android.view.**