LIHADOOP-42762 Change the version in /external/avro/pom.xml to be 2.3.0

RB=1514282
BUG=LIHADOOP-42762
G=superfriends-reviewers
R=fli,mshen,yezhou,edlu
A=fli

Author: Yuxiang Chen

external/avro/pom.xml

@@ -21,7 +21,7 @@
   <parent>
     <groupId>org.apache.spark</groupId>
     <artifactId>spark-parent_2.11</artifactId>
-    <version>2.4.0-SNAPSHOT</version>
+    <version>2.3.0</version>
     <relativePath>../../pom.xml</relativePath>
   </parent>