changed role to class in passthroughs

ch11_blockchain.adoc

@@ -118,7 +118,7 @@ The primary identifier of a block
 is its cryptographic hash, a commitment made by hashing the
 block header twice through the SHA256 algorithm. The resulting 32-byte
 hash is called the _block hash_ but is more accurately the _block header
-hash_, pass:[<span role="keep-together">because only the block header is
+hash_, pass:[<span class="keep-together">because only the block header is
 used to compute it. For example,</span>]
 +000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f+ is
 the block hash of the first block on Bitcoin's blockchain. The block hash
@@ -133,9 +133,9 @@ separate database table as part of the block's metadata, to facilitate
 indexing and faster retrieval of blocks from disk.
 
 A second way to identify a block is by its position in the blockchain,
-called the pass:[<span role="keep-together"><em>block height</em>. The
+called the pass:[<span class="keep-together"><em>block height</em>. The
 genesis block is at block height 0 (zero) and is the</span>]
-pass:[<span role="keep-together">same block that was previously
+pass:[<span class="keep-together">same block that was previously
 referenced by the following block hash</span>]
 +000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f+. A
 block can thus be identified in two ways: by referencing the block hash