Fix java install docs (#15250)

Author: zachgk

docs/install/java_setup.md

@@ -43,7 +43,7 @@ brew install maven
 Please run the following lines:
 
 ```bash
-sudo apt-get install openjdk-8-java maven
+sudo apt-get install openjdk-8-jdk maven
 ```
 
 **Step 2.** Run the demo MXNet-Java project.

docs/tutorials/java/mxnet_java_on_intellij.md

@@ -44,7 +44,7 @@ brew install opencv
 Run the following commands to install the prerequisites on Ubuntu.
 
 ```
-sudo apt-get install openjdk-8-java maven
+sudo apt-get install openjdk-8-jdk maven
 ```