[BUILD] Reference fasterxml.jackson.version in sql/core/pom.xml

Author: tedyu <yuzhihong@gmail.com>

Closes #6031 from tedyu/master and squashes the following commits:

5c2580c [tedyu] Reference fasterxml.jackson.version in sql/core/pom.xml
ff2a44f [tedyu] Merge branch 'master' of github.com:apache/spark
28c8394 [tedyu] Upgrade version of jackson-databind in sql/core/pom.xml

sql/core/pom.xml

@@ -64,7 +64,7 @@
     <dependency>
       <groupId>com.fasterxml.jackson.core</groupId>
       <artifactId>jackson-databind</artifactId>
-      <version>2.4.4</version>
+      <version>${fasterxml.jackson.version}</version>
     </dependency>
     <dependency>
       <groupId>org.jodd</groupId>