add java10 in travis dot yml

[lovepoem]

What is the purpose of the change

add add java10 in travis dot yml
#1521

Brief changelog

.travis.yml
pom.xml

Verifying this change

ci pass

[codecov-io]

Codecov Report

Merging #1913 into master will increase coverage by 0.01%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master    #1913      +/-   ##
============================================
+ Coverage      49.5%   49.51%   +0.01%     
+ Complexity     4506     4504       -2     
============================================
  Files           558      558              
  Lines         24344    24347       +3     
  Branches       4315     4315              
============================================
+ Hits          12051    12055       +4     
+ Misses        10435    10431       -4     
- Partials       1858     1861       +3

Impacted Files	Coverage Δ	Complexity Δ
...ba/dubbo/registry/multicast/MulticastRegistry.java	56.06% <0%> (-1.68%)	38% <0%> (-3%)
...ba/dubbo/remoting/transport/netty/NettyClient.java	72.88% <0%> (-1.26%)	12% <0%> (ø)
...a/dubbo/remoting/transport/netty4/NettyClient.java	63.33% <0%> (-1.08%)	11% <0%> (ø)
...baba/dubbo/remoting/transport/mina/MinaClient.java	58.46% <0%> (+0.64%)	9% <0%> (+1%)	⬆️
.../com/alibaba/dubbo/monitor/dubbo/DubboMonitor.java	89.71% <0%> (+1.86%)	15% <0%> (ø)	⬇️
...onfig/spring/extension/SpringExtensionFactory.java	84.61% <0%> (+19.23%)	8% <0%> (ø)	⬇️

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