Fix crash on some old Android JVMs (issue #2)

Author: akaita

src/main/java/hu/akarnokd/rxjava2/debug/RxJavaAssemblyException.java

@@ -103,6 +103,8 @@ public String stacktrace() {
     @Override
     public synchronized Throwable fillInStackTrace() {
         // don't store own stacktrace
+        // empty stacktrace prevents crashes on some JVMs when `getStackTrace()` is invoked
+        setStackTrace(new StackTraceElement[0]);
         return this;
     }