Fix ambiguous dox: you only need JRE, not JDK [ci skip]

docs/operations-guide/running-the-metabase-jar-file.md

 # Running the Metabase Jar File
 
-To run the Metabase jar file you need to have Java installed on your system. Currently Metabase requires Java 8 or higher and will work on either the OpenJDK or Oracle JDK.
+To run the Metabase jar file you need to have Java installed on your system. Currently Metabase requires Java 8 or higher and will work on either the OpenJDK or Oracle JRE.
 
 ### Download Metabase
 
@@ -19,7 +19,7 @@ You should see output such as:
     Java(TM) SE Runtime Environment (build 1.8.0_31-b13)
     Java HotSpot(TM) 64-Bit Server VM (build 25.31-b07, mixed mode)
 
-If you did not see the output above and instead saw either an error or your Java version is less than 1.8, then you need to install the Java Runtime.
+If you did not see the output above and instead saw either an error or your Java version is less than 1.8, then you need to install the Java Runtime (JRE).
 
 [OpenJDK Downloads](http://openjdk.java.net/install/)
 [Oracle's Java Downloads](http://www.oracle.com/technetwork/java/javase/downloads/index.html)