Fix deprecated warnings in Ruby 2.4.0+ (#415)

lib/annotate/annotate_models.rb

@@ -168,7 +168,7 @@ module AnnotateModels
       when NilClass                 then 'NULL'
       when TrueClass                then 'TRUE'
       when FalseClass               then 'FALSE'
-      when Float, Fixnum, Bignum    then value.to_s
+      when Float, Integer           then value.to_s
         # BigDecimals need to be output in a non-normalized form and quoted.
       when BigDecimal               then value.to_s('F')
       when Array                    then value.map {|v| quote(v)}