ch02: fix new "Alice tx included in a block" image

ch02.asciidoc

@@ -270,7 +270,7 @@ You can see the block that includes https://blockchain.info/btc/block/277316[Ali
 ((("genesis block")))((("blocks", "genesis block")))((("blockchain (the)", "genesis block")))In the diagram in <<block-alice1>>,  we can see block #277316, which contains Alice's transaction. Below it are 277,316 blocks (including block #0), linked to each other in a chain of blocks (blockchain) all the way back to block #0, known as the _genesis block_. Over time, as the "height" in blocks increases, so does the computation difficulty for each block and the chain as a whole. The blocks mined after the one that contains Alice's transaction act as further assurance, as they pile on more computation in a longer and longer chain. By convention, any block with more than six confirmations is considered irrevocable, because it would require an immense amount of computation to invalidate and recalculate six blocks. We will examine the process of mining and the way it builds trust in more detail in <<mining>>.((("", startref="BToverview02")))((("", startref="MACover02")))
 
 [[block-alice1]]
-.Alice's transaction included in block #277316 (triangle block)
+.Alice's transaction included in block #277316
 image::images/mbc2_0209.png["Alice's transaction included in a block"]
 
 === Spending the Transaction