Exclude commons-codec and commons-io from assembled JAR

Consumers of MXNet are exposed to the commons-codec and commons-io library versions MXNet uses internally. This change excludes those JARs from the JARs created with `make scalapkg`.

Alternative could be using the Maven Shade Plugin but that may be more hassle in the long term than its worth: https://maven.apache.org/plugins/maven-shade-plugin/

scala-package/assembly/src/main/assembly/assembly.xml

@@ -10,6 +10,8 @@
         <include>*:*:jar</include>
       </includes>
       <excludes>
+        <exclude>commons-codec:</exclude>
+        <exclude>commons-io:*</exclude>
         <exclude>org.scala-lang:*</exclude>
         <exclude>org.scala-lang.modules:*</exclude>
       </excludes>