Fix float issue with object space dump (#146)

I get `NoMethodError` when doing a diff against a float constant because of how `ObjectSpace.dump(object)` treats floats.

```
# here is the problematic line in helpers.rb
address = JSON.parse(ObjectSpace.dump(object))["address"]

ObjectSpace.dump(1.0)
=> "1.00000"
```

This fixes that.

Author: ransombriggs

lib/super_diff/helpers.rb

@@ -52,8 +52,12 @@ def object_address_for(object)
 
       def object_address_for(object)
         # Sources: <https://bugs.ruby-lang.org/issues/15408> and <https://bugs.ruby-lang.org/issues/15626#Object-ID>
-        address = JSON.parse(ObjectSpace.dump(object))["address"]
-        "0x%016x" % Integer(address, 16)
+        json = JSON.parse(ObjectSpace.dump(object))
+        if json.is_a?(Hash)
+          "0x%016x" % Integer(json["address"], 16)
+        else
+          ""
+        end
       end
     else
       def object_address_for(object)

spec/unit/helpers_spec.rb

@@ -39,6 +39,20 @@
         end
       end
     end
+
+    describe "object_address_for" do
+      if SuperDiff::Helpers.ruby_version_matches?(">= 2.7.0")
+        it "returns an empty string for Floats" do
+          expect(helper.object_address_for(1.0)).to eq("")
+        end
+
+        it "returns an object address for Objects" do
+          object = Object.new
+          address = JSON.parse(ObjectSpace.dump(object))["address"]
+          expect(helper.object_address_for(object)).to eq("0x%016x" % Integer(address, 16))
+        end
+      end
+    end
   end
 
   describe 'as class methods' do