Imp & Fix: issue #217

[fangyincheng]

What this PR does:

1. update getty&hessian version
2. fix bug about registryProtocol.Export
3. fix bug for failover_cluster_invoker.go

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

[hxmhlt]

LGTM

[AlexStocks]

the title is improper. it should be "Fix: issue xxx"

[codecov-io]

Codecov Report

Merging #212 into develop will decrease coverage by 0.14%.
The diff coverage is 38.46%.

@@             Coverage Diff             @@
##           develop     #212      +/-   ##
===========================================
- Coverage    66.11%   65.96%   -0.15%     
===========================================
  Files           96       96              
  Lines         6455     6459       +4     
===========================================
- Hits          4268     4261       -7     
- Misses        1743     1751       +8     
- Partials       444      447       +3

Impacted Files	Coverage Δ
cluster/cluster_impl/failover_cluster_invoker.go	72.34% <0%> (-6.73%)	⬇️
registry/protocol/protocol.go	81.73% <100%> (ø)	⬆️
protocol/dubbo/readwriter.go	70.37% <50%> (ø)	⬆️
protocol/jsonrpc/server.go	59.79% <0%> (-1.51%)	⬇️
remoting/zookeeper/listener.go	46.9% <0%> (-1.04%)	⬇️
remoting/zookeeper/client.go	63.87% <0%> (-0.58%)	⬇️

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[fangyincheng]

the title is improper. it should be "Fix: issue xxx"

don't have this issue.Add?