Download page seems broken

[Wangda Tan]

Hi Submarine Dev,

Download page (http://submarine.apache.org/download.html#) seems broken:
*Download Apache Submarine*

*The latest release of Apache Submarine is 0.3.0.*

   -

   *Apache Submarine 0.3.0 released on Nov 23, 2019 (release notes
   <https://github.com/apache/submarine/blob/master/docs/helper/release.md>)
   (git tag <http://submarine.apache.org/download.html#>)*
   - *Binary package (Install guide
      <https://github.com/apache/submarine/blob/master/docs/helper/install.md>):
*

- * (120 MB, checksum <http://submarine.apache.org/download.html#>,
signature <http://submarine.apache.org/download.html#>, Announcement
<http://submarine.apache.org/download.html#>)*
- *Source: ** (12 MB, checksum
<http://submarine.apache.org/download.html#>, signature
<http://submarine.apache.org/download.html#>)*

All link seems not work.

Also, IIRC, Submarine 0.3.0 is not released yet, I think we should call it
0.3.0-SNAPSHOT.

Thoughts?

Thanks,
Wangda