upgrade hessian2: support decimal

[wongoo]

What this PR does:
Add support for decimal
Which issue(s) this PR fixes:

Fixes #109

Special notes for your reviewer:
None

Does this PR introduce a user-facing change?:

- add support for decimal

[codecov-io]

Codecov Report

Merging #126 into master will decrease coverage by 0.11%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #126      +/-   ##
==========================================
- Coverage   67.83%   67.71%   -0.12%     
==========================================
  Files          69       69              
  Lines        4349     4349              
==========================================
- Hits         2950     2945       -5     
- Misses       1098     1103       +5     
  Partials      301      301

Impacted Files	Coverage Δ
protocol/dubbo/listener.go	53.66% <0%> (-2.3%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update b6bbe67...9d03820. Read the comment docs.