fix C2 may not send during rtmp handshake

library/src/main/java/com/github/faucamp/simplertmp/io/RtmpConnection.java

@@ -94,6 +94,7 @@ public class RtmpConnection implements RtmpPublisher {
         handshake.readS0(in);
         handshake.readS1(in);
         handshake.writeC2(out);
+        out.flush();
         handshake.readS2(in);
     }

library/src/main/java/com/github/faucamp/simplertmp/packets/Handshake.java

@@ -162,7 +162,7 @@ public final class Handshake {
     /** Generates and writes the third handshake packet (C2) */
     public final void writeC2(OutputStream out) throws IOException {
-        Log.d(TAG, "readC2");
+        Log.d(TAG, "writeC2");
         // C2 is an echo of S1
         if (s1 == null) {
             throw new IllegalStateException("C2 cannot be written without S1 being read first");