Update README.md (#763)

Update the version of the project to   2.7.8   .
diff --git a/README.md b/README.md
index d85bf08..2ebdf45 100644
--- a/README.md
+++ b/README.md
@@ -19,7 +19,7 @@
 ```xml
 <properties>
     <spring-boot.version>2.3.0.RELEASE</spring-boot.version>
-    <dubbo.version>2.7.7</dubbo.version>
+    <dubbo.version>2.7.8</dubbo.version>
 </properties>
     
 <dependencyManagement>
@@ -50,7 +50,7 @@
     <dependency>
         <groupId>org.apache.dubbo</groupId>
         <artifactId>dubbo-spring-boot-starter</artifactId>
-        <version>2.7.7</version>
+        <version>2.7.8</version>
     </dependency>    
 </dependencies>
 ```