deps: update dependency com.google.protobuf:protobuf-java to v3.12.0

[renovate-bot]

This PR contains the following updates:

Package	Update	Change
com.google.protobuf:protobuf-java	minor	3.11.4 -> 3.12.0

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[codecov]

Codecov Report

Merging #168 into master will increase coverage by 10.34%.
The diff coverage is n/a.

@@              Coverage Diff              @@
##             master     #168       +/-   ##
=============================================
+ Coverage     67.94%   78.29%   +10.34%     
- Complexity      201      236       +35     
=============================================
  Files             6        6               
  Lines          1273     2216      +943     
  Branches          9       37       +28     
=============================================
+ Hits            865     1735      +870     
- Misses          366      432       +66     
- Partials         42       49        +7     

Impacted Files	Coverage Δ	Complexity Δ
...alabeling/v1beta1/DataLabelingServiceSettings.java	6.48% <0.00%> (-0.13%)	2.00% <0.00%> (ø%)
...atalabeling/v1beta1/DataLabelingServiceClient.java	65.54% <0.00%> (+2.02%)	137.00% <0.00%> (+33.00%)
...ling/v1beta1/stub/GrpcDataLabelingServiceStub.java	96.98% <0.00%> (+3.81%)	42.00% <0.00%> (+1.00%)
.../v1beta1/stub/DataLabelingServiceStubSettings.java	84.44% <0.00%> (+7.29%)	50.00% <0.00%> (+1.00%)

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