Merge pull request #61 from greenteaisgreat/greenteaisgreat-patch-1

Correct grammar for intro.adoc

Author: hi-liang

chapters/intro.adoc

@@ -5,7 +5,7 @@ You are going to have real fun here. And, you will gain the ability to do impres
 
 A common mobile device, the one you might have in your hands right now, can have 100,000 times more computing power than the computer used to send humans to the moon for the first time. There are 7.7 billion humans; did you know that by 2020 there will be more than 30 billion devices connected to the Internet? Imagine all that power... you could do many unprecedented things with only a little part of it, and that power keeps growing everyday...
 
-Our world depends on computers. Imagine the apocalyptic catastrophe if computers ceased to work: money in banks is inaccessible, all telecommunications die, airports cease functioning and commercial airliners would  fall from the sky, energy distribution systems become uncontrollable, hospitals and critical life support systems would irrevocably fail, and our society would collapse. In 1988, a single person, without bad intentions, took down all the Internet with just one malicious program, known as the Morris Worm. Society was different at that time so it was not as catastrophic as it would have been now. But, why we have not collapsed yet? 
+Our world depends on computers. Imagine the apocalyptic catastrophe if computers ceased to work: money in banks is inaccessible, all telecommunications die, airports cease functioning and commercial airliners would  fall from the sky, energy distribution systems become uncontrollable, hospitals and critical life support systems would irrevocably fail, and our society would collapse. In 1988, a single person, without bad intentions, took down all the Internet with just one malicious program, known as the Morris Worm. Society was different at that time so it was not as catastrophic as it would have been now. But, why have we not collapsed yet? 
 
 The only way to overcome a weakness is to first know that it exists. Hackers find weaknesses in the computer world. The word hacker has had several definitions throughout history. In a dictionary, we can find two related definitions: