Update JAVA_OPTS documentation
Update JAVA_OPTS documentation

Previously the JAVA_OPTS documentation erroneously stated that there were a
set of allowed and disallowed memory arguments.  With the advent of the new
memory calculator all flags are now allowed.  This change updates the docs to
reflect that.

[resolves #520]

tom-collings/jboss-buildpack,stipx/java-buildpack,PatrikSteuer/java-buildpack,stipx/java-buildpack,rakutentech/java-buildpack,cloudfoundry-community/jboss-buildpack,tom-collings/jboss-buildpack,svenfrauen/java-buildpack,hmlingesh/java-buildpack,waltersve/java-buildpack,Appdynamics/java-buildpack,rakutentech/java-buildpack,Appdynamics/java-buildpack,hmlingesh/java-buildpack,waltersve/java-buildpack,svenfrauen/java-buildpack,hmlingesh/java-buildpack,cloudfoundry-community/tomee-buildpack,cloudfoundry-community/jboss-buildpack,cloudfoundry-community/tomee-buildpack,PatrikSteuer/java-buildpack,cloudfoundry/java-buildpack,cloudfoundry/java-buildpack,hmlingesh/java-buildpack