Update master-slave section anchor (#129)

solutions/system_design/query_cache/README.md

@@ -247,7 +247,7 @@ To handle the heavy request load and the large amount of memory needed, we'll sc
 
 ### SQL scaling patterns
 
-* [Read replicas](https://github.com/donnemartin/system-design-primer#master-slave)
+* [Read replicas](https://github.com/donnemartin/system-design-primer#master-slave-replication)
 * [Federation](https://github.com/donnemartin/system-design-primer#federation)
 * [Sharding](https://github.com/donnemartin/system-design-primer#sharding)
 * [Denormalization](https://github.com/donnemartin/system-design-primer#denormalization)

solutions/system_design/scaling_aws/README.md

@@ -344,7 +344,7 @@ We can further separate out our [**Application Servers**](https://github.com/don
 
 ### SQL scaling patterns
 
-* [Read replicas](https://github.com/donnemartin/system-design-primer#master-slave)
+* [Read replicas](https://github.com/donnemartin/system-design-primer#master-slave-replication)
 * [Federation](https://github.com/donnemartin/system-design-primer#federation)
 * [Sharding](https://github.com/donnemartin/system-design-primer#sharding)
 * [Denormalization](https://github.com/donnemartin/system-design-primer#denormalization)

solutions/system_design/social_graph/README.md

@@ -290,7 +290,7 @@ Below are further optimizations:
 
 ### SQL scaling patterns
 
-* [Read replicas](https://github.com/donnemartin/system-design-primer#master-slave)
+* [Read replicas](https://github.com/donnemartin/system-design-primer#master-slave-replication)
 * [Federation](https://github.com/donnemartin/system-design-primer#federation)
 * [Sharding](https://github.com/donnemartin/system-design-primer#sharding)
 * [Denormalization](https://github.com/donnemartin/system-design-primer#denormalization)

solutions/system_design/web_crawler/README.md

@@ -294,7 +294,7 @@ Below are a few other optimizations to the **Crawling Service**:
 
 ### SQL scaling patterns
 
-* [Read replicas](https://github.com/donnemartin/system-design-primer#master-slave)
+* [Read replicas](https://github.com/donnemartin/system-design-primer#master-slave-replication)
 * [Federation](https://github.com/donnemartin/system-design-primer#federation)
 * [Sharding](https://github.com/donnemartin/system-design-primer#sharding)
 * [Denormalization](https://github.com/donnemartin/system-design-primer#denormalization)