KOBAYASHI Shuji 80965fe2d7 Fix message of ThrowCatchJump in mruby-catch gem ...

### Example

```ruby
begin
  throw 1
rescue Exception => e
  puts e.message
end
```

#### Before this patch:

```console
$ bin/mruby example.rb
uncaught throw :1
```
#### After this patch (same as Ruby):

```console
$ bin/mruby example.rb
uncaught throw 1
```

2021-02-05 23:14:58 +09:00

..

catch.rb

Fix message of ThrowCatchJump in mruby-catch gem

2021-02-05 23:14:58 +09:00