Fix travis error (Satoshi-style double space after period)

ch01.asciidoc

@@ -30,7 +30,7 @@ The `nSequence` field was intended to allow users to transmit updated versions o
 Such a payment channel would then be valid as long as the transaction was not mined.
 According to a Mailinglist post in 2013 by early Bitcoin developer Mike Hearn, Satoshi Nakamoto envisioned this construction for the use case of high frequency trading.footnote:HearnBitcoinDev[Mike Hearn on Bitcoin-dev - April 16th 2013 - Anti DoS for tx replacement http://web.archive.org/web/20190501234757/https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2013-April/002433.html.]
 
-However, there were some weaknesses in this initial formulation that limited its potential. Firstly, the payment channel would only be open until the transaction was mined in a block, either limiting the duration the payment channel or handing control of the payment channel to the miners.  Secondly, there was no economic incentive for miners to respect the `nSequence` number, rendering this mechanism effectively useless.
+However, there were some weaknesses in this initial formulation that limited its potential. Firstly, the payment channel would only be open until the transaction was mined in a block, either limiting the duration the payment channel or handing control of the payment channel to the miners. Secondly, there was no economic incentive for miners to respect the `nSequence` number, rendering this mechanism effectively useless.
 
 The Revocable Sequence Maturity Contracts (RSMC), which formed payment channels in the first version of the Lightning Network, reference in their name the fact that they fixed this weakness of the `nSequence` field.
 This is achieved by creating an economic incentive via a penalty mechanism; otherwise, the most recent transaction or update in the payment channel is published to the Bitcoin network, and becomes enforcable in this way.