CH11: small correction to relative size diff between header and block

Thanks Murchandamus

ch09.asciidoc

@@ -77,7 +77,7 @@ block is made of a header, containing metadata, followed by a long list
 of transactions that make up the bulk of its size. The block header is
 80 bytes, whereas the total size of all transactions in a block can be
 up to about 4,000,000 bytes.  A complete block,
-with all transactions, can therefore be over 50,000 times larger than the block
+with all transactions, can therefore be almost 50,000 times larger than the block
 header. <<block_structure1>> describes how Bitcoin Core stores the structure of a block.
 
 [[block_structure1]]