Fixes error for StdErr.puts <number>

error: String can't be coerced into Fixnum (TypeError)

lib/kidsruby/stdio.rb

@@ -22,7 +22,7 @@ def write(data)
   end
 
   def puts(data)
-    write(data + "\n")
+    write(data.to_s + "\n")
   end
 end
 

spec/models/std_io_spec.rb

@@ -11,3 +11,12 @@
   end
 end
 
+describe StdErr do
+  describe ".puts" do
+    it "should delegate the coerced, newlined data to .write" do
+      stderr_ut = StdErr.new
+      stderr_ut.expects(:write).with("234\n")
+      stderr_ut.puts(234)
+    end
+  end
+end