rm java 9 and 10 on travis

[diecui1202]

What is the purpose of the change

fix #2558 , rm java 9 and 10 on travis

Brief changelog

XXXXX

Verifying this change

XXXXX

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[codecov-io]

Codecov Report

Merging #2559 into master will decrease coverage by 0.08%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master    #2559      +/-   ##
============================================
- Coverage        55%   54.92%   -0.09%     
+ Complexity     5279     5276       -3     
============================================
  Files           573      573              
  Lines         25517    25517              
  Branches       4531     4531              
============================================
- Hits          14035    14014      -21     
- Misses         9381     9399      +18     
- Partials       2101     2104       +3

Impacted Files	Coverage Δ	Complexity Δ
...ache/dubbo/remoting/p2p/support/AbstractGroup.java	45.45% <0%> (-11.37%)	7% <0%> (-1%)
...e/dubbo/remoting/transport/netty/NettyChannel.java	57.5% <0%> (-8.75%)	19% <0%> (-2%)
...ubbo/rpc/protocol/dubbo/ChannelWrappedInvoker.java	41.66% <0%> (-8.34%)	3% <0%> (ø)
...onfig/spring/extension/SpringExtensionFactory.java	79.31% <0%> (-6.9%)	11% <0%> (ø)
...he/dubbo/remoting/transport/netty/NettyServer.java	67.85% <0%> (-3.58%)	8% <0%> (-1%)
...a/org/apache/dubbo/monitor/dubbo/DubboMonitor.java	87.85% <0%> (-1.87%)	15% <0%> (ø)
.../dubbo/remoting/transport/netty4/NettyChannel.java	62.35% <0%> (+1.17%)	23% <0%> (+1%)	⬆️

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