Require Java 9 for JVM backend

.travis.yml

@@ -21,7 +21,7 @@ addons:
     - gcc-6
 
 script:
-    - if [[ $TRAVIS_OS_NAME != osx && $RAKUDO_OPTIONS =~ jvm ]]; then sudo -E apt-get install oracle-java8-installer; fi
+    - if [[ $TRAVIS_OS_NAME != osx && $RAKUDO_OPTIONS =~ jvm ]]; then sudo -E apt-get install oracle-java9-installer; fi
     - perl Configure.pl $RAKUDO_OPTIONS --moar-option=--cc=$(command -v gcc-6 >/dev/null 2>&1; if [ $? -eq 1 ]; then printf "gcc"; else printf "gcc-6"; fi)
     - "make install"
     - (cd ~/build/rakudo/rakudo/ && prove -e ~/build/rakudo/rakudo/install/bin/perl6 -vlr t)

tools/templates/jvm/Makefile.in

@@ -90,7 +90,7 @@ check_@backend_prefix@_nqp_version: @@script(check-nqp-version.pl)@@
 
 $(RUNTIME_JAR): $(RUNTIME_JAVAS)
 	$(MKPATH) bin
-	$(JAVAC) -source 1.8 -cp @q($(BLD_NQP_JARS))@ -g -d bin -encoding UTF8 $(RUNTIME_JAVAS)
+	$(JAVAC) -source 1.9 -cp @q($(BLD_NQP_JARS))@ -g -d bin -encoding UTF8 $(RUNTIME_JAVAS)
 	$(JAR) cf0 rakudo-runtime.jar -C bin@slash@ .
 
 $(PERL6_ML_JAR): @nfpl(src/Perl6/ModuleLoader.nqp src/vm/jvm/ModuleLoaderVMConfig.nqp src/vm/jvm/Perl6/JavaModuleLoader.nqp gen/nqp-version)@