chore: Update README for 2.0.0 (#224)

Author: acioc

README.md

@@ -56,7 +56,7 @@ You can get the latest release from Maven:
 <dependency>
   <groupId>com.amazonaws</groupId>
   <artifactId>aws-encryption-sdk-java</artifactId>
-  <version>1.7.0</version>
+  <version>2.0.0</version>
 </dependency>
 ```