RFR: JDK-8226412: Fix command-line help text for javac -target

[Jonathan Gibbons]

Please review a small resource-bundle fix for the command-line help for 
javac --release, --source, --target, to make them consistent in their 
terminology, with each other and with related documentation.

-- Jon

JBS: https://bugs.openjdk.java.net/browse/JDK-8226412
Webrev: http://cr.openjdk.java.net/~jjg/8226412-command-line-help/webrev.00/