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
```
MODIFY
mrbgems/mruby-catch/mrblib/catch.rb
mrbgems/mruby-catch/mrblib/catch.rb
@@ -2,7 +2,7 @@ class ThrowCatchJump < Exception
def initialize(tag, val)
@tag = tag
@val = val
- super("uncaught throw :#{tag}")
+ super("uncaught throw #{tag.inspect}")
end
def _tag
@tag

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
```