Fix typo in Twitter timeline and search solution (donnemartin#251)

solutions/system_design/twitter/README.md

@@ -249,7 +249,7 @@ We'll introduce some components to complete the design and to address scalabilit
 
 The **Fanout Service** is a potential bottleneck.  Twitter users with millions of followers could take several minutes to have their tweets go through the fanout process.  This could lead to race conditions with @replies to the tweet, which we could mitigate by re-ordering the tweets at serve time.
 
-We could also avoid fanning out tweets from highly-followed users.  Instead, we could search to find tweets for high-followed users, merge the search results with the user's home timeline results, then re-order the tweets at serve time.
+We could also avoid fanning out tweets from highly-followed users.  Instead, we could search to find tweets for highly-followed users, merge the search results with the user's home timeline results, then re-order the tweets at serve time.
 
 Additional optimizations include: