warn user before build expires

Closes #4322
// FREEBIE

src/org/thoughtcrime/securesms/jobs/SendJob.java

@@ -34,7 +34,7 @@ public abstract class SendJob extends MasterSecretJob {
 
   @Override
   public final void onRun(MasterSecret masterSecret) throws Exception {
-    if (!Util.isBuildFresh()) {
+    if (Util.getDaysTillBuildExpiry() <= 0) {
       throw new TextSecureExpiredException(String.format("TextSecure expired (build %d, now %d)",
                                                          BuildConfig.BUILD_TIMESTAMP,
                                                          System.currentTimeMillis()));