Unify overflow error class for conversion to integer to `RangeError`

src/numeric.c

@@ -1230,7 +1230,7 @@ mrb_flo_to_fixnum(mrb_state *mrb, mrb_value x)
       z = (mrb_int)d;
     }
     else {
-      mrb_raisef(mrb, E_ARGUMENT_ERROR, "number (%S) too big for integer", x);
+      mrb_raisef(mrb, E_RANGE_ERROR, "number (%S) too big for integer", x);
     }
   }
   return mrb_fixnum_value(z);

src/string.c

@@ -2115,7 +2115,7 @@ mrb_str_len_to_inum(mrb_state *mrb, const char *str, mrb_int len, mrb_int base,
       else
 #endif
       {
-        mrb_raisef(mrb, E_ARGUMENT_ERROR, "string (%S) too big for integer",
+        mrb_raisef(mrb, E_RANGE_ERROR, "string (%S) too big for integer",
                    mrb_str_new(mrb, str, pend-str));
       }
     }