Fix typo in part 1.2

Author: galcyurio

Part 1 - Getting Started/2. Key types.md

@@ -129,7 +129,7 @@ Late: 2
 Late: 3
 ```
 
-Our late subscriber now missed the first value, which fell off the buffer of size 2. Similarily, old values fall off the buffer as time passes, when the subject is created with `createWithTime`
+Our late subscriber now missed the first value, which fell off the buffer of size 2. Similarly, old values fall off the buffer as time passes, when the subject is created with `createWithTime`.
 
 ```java
 ReplaySubject<Integer> s = ReplaySubject.createWithTime(150, TimeUnit.MILLISECONDS,