Fix doc typos

[gwenneg]

Here's another round of doc typos fixing.

[codecov]

Codecov Report

Merging #480 (cb59926) into master (7998aa2) will increase coverage by 0.26%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master     #480      +/-   ##
============================================
+ Coverage     89.84%   90.11%   +0.26%     
- Complexity     2914     2920       +6     
============================================
  Files           381      381              
  Lines         11297    11297              
  Branches       1417     1419       +2     
============================================
+ Hits          10150    10180      +30     
+ Misses          583      565      -18     
+ Partials        564      552      -12     

Impacted Files	Coverage Δ	Complexity Δ
...in/java/io/smallrye/mutiny/groups/MultiOnItem.java	100.00% <ø> (ø)	53.00 <0.00> (ø)
.../io/smallrye/mutiny/helpers/queues/DrainUtils.java	77.77% <0.00%> (-4.45%)	12.00% <0.00%> (-1.00%)
...io/smallrye/mutiny/operators/uni/UniMemoizeOp.java	93.06% <0.00%> (ø)	27.00% <0.00%> (ø%)
...java/io/smallrye/mutiny/helpers/Subscriptions.java	78.45% <0.00%> (+1.10%)	47.00% <0.00%> (+1.00%)
...mallrye/mutiny/operators/multi/MultiFlatMapOp.java	86.29% <0.00%> (+1.24%)	3.00% <0.00%> (ø%)
...y/operators/multi/processors/UnicastProcessor.java	97.34% <0.00%> (+1.76%)	45.00% <0.00%> (+1.00%)
...perators/multi/processors/SerializedProcessor.java	92.07% <0.00%> (+1.98%)	26.00% <0.00%> (+1.00%)
...rye/mutiny/converters/uni/UniToMultiPublisher.java	91.66% <0.00%> (+2.77%)	2.00% <0.00%> (ø%)
...operators/multi/builders/CollectionBasedMulti.java	93.44% <0.00%> (+3.27%)	4.00% <0.00%> (ø%)
...tiny/operators/multi/MultiBufferWithTimeoutOp.java	72.03% <0.00%> (+5.93%)	3.00% <0.00%> (ø%)
... and 2 more

[jponge]

Thank you!