Fix typo (vuejs#434)

docs/en/intro.md

@@ -44,7 +44,7 @@ However, the simplicity quickly breaks down when we have **multiple components t
 - Multiple views may depend on the same piece of state.
 - Actions from different views may need to mutate the same piece of state.
 
-For problem one, passing props can be tedious for deeply nested components, and simply doesn't work for sibling components. For problem two, we often find ourselves resorting to solutions such as reaching for direct parent/child instance references or trying to mutate and synchronize multiple copies of the state via events. Both of these patterns are brittle and quickly leads to unmaintainable code.
+For problem one, passing props can be tedious for deeply nested components, and simply doesn't work for sibling components. For problem two, we often find ourselves resorting to solutions such as reaching for direct parent/child instance references or trying to mutate and synchronize multiple copies of the state via events. Both of these patterns are brittle and quickly lead to unmaintainable code.
 
 So why don't we extract the shared state out of the components, and manage it in a global singleton? With this, our component tree becomes a big "view", and any component can access the state or trigger actions, no matter where they are in the tree!