Add missing specialization for Float#instance_variables

Author: bjfish

spec/ruby/core/kernel/instance_variables_spec.rb

@@ -4,7 +4,9 @@
 describe "Kernel#instance_variables" do
   describe "immediate values" do
     it "returns an empty array if no instance variables are defined" do
-      0.instance_variables.should == []
+      [0, 0.5, true, false, nil].each do |value|
+        value.instance_variables.should == []
+      end
     end
 
     it "returns the correct array if an instance variable is added" do

src/main/java/org/truffleruby/core/support/TypeNodes.java

@@ -159,6 +159,11 @@ protected RubyArray instanceVariables(long object) {
             return ArrayHelpers.createEmptyArray(getContext());
         }
 
+        @Specialization
+        protected RubyArray instanceVariables(double object) {
+            return ArrayHelpers.createEmptyArray(getContext());
+        }
+
         @Specialization
         protected RubyArray instanceVariables(boolean object) {
             return ArrayHelpers.createEmptyArray(getContext());