Update outdated java example in wiki #6331

[ozcanyus]

Updated java example in docs/How-To-Use-RxJava.md file with java 8 version.

Resolves: #6331

[codecov]

Codecov Report

Merging #6351 into 2.x will decrease coverage by 0.05%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##                2.x    #6351      +/-   ##
============================================
- Coverage     98.27%   98.22%   -0.06%     
- Complexity     6285     6286       +1     
============================================
  Files           672      672              
  Lines         44990    44990              
  Branches       6223     6223              
============================================
- Hits          44214    44191      -23     
- Misses          246      259      +13     
- Partials        530      540      +10

Impacted Files	Coverage Δ	Complexity Δ
...ex/internal/operators/flowable/FlowableCreate.java	90% <0%> (-6.46%)	6% <0%> (ø)
...l/operators/observable/ObservableFlatMapMaybe.java	90.84% <0%> (-3.93%)	2% <0%> (ø)
...nternal/operators/observable/ObservableCreate.java	94.87% <0%> (-3.42%)	2% <0%> (ø)
...tivex/internal/schedulers/TrampolineScheduler.java	96.1% <0%> (-2.6%)	6% <0%> (ø)
...ex/internal/subscriptions/SubscriptionArbiter.java	97.47% <0%> (-2.53%)	50% <0%> (-1%)
...x/internal/operators/flowable/FlowablePublish.java	96.59% <0%> (-2.13%)	11% <0%> (ø)
.../io/reactivex/internal/schedulers/IoScheduler.java	89.36% <0%> (-1.07%)	9% <0%> (ø)
...perators/mixed/ObservableSwitchMapCompletable.java	98.94% <0%> (-1.06%)	3% <0%> (ø)
...rnal/operators/flowable/FlowableSkipLastTimed.java	96.93% <0%> (-1.03%)	2% <0%> (ø)
...ernal/operators/flowable/FlowableTimeoutTimed.java	98.37% <0%> (-0.82%)	3% <0%> (ø)
... and 18 more

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[akarnokd]

I'd instead show a Consumer<String> and the lambda version, similar to the hello world example.

[ozcanyus]

Updated similar to hello world example.