bump datadog-ci dependency from 0.2.0 to 0.3.0

[anmarchenko]

What does this PR do?
Bump datadog-ci dep in gemspec to 0.3.0

Motivation:
New datadog-ci version is released

For Datadog employees:

• If this PR touches code that signs or publishes builds or packages, or handles
  credentials of any kind, I've requested a review from @DataDog/security-design-and-guidance.
• This PR doesn't touch any of that.

Unsure? Have a question? Request a review!

[codecov-commenter]

Codecov Report

Merging #3223 (280e760) into master (e67840f) will increase coverage by 0.00%.
Report is 10 commits behind head on master.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #3223   +/-   ##
=======================================
  Coverage   98.21%   98.22%           
=======================================
  Files        1252     1252           
  Lines       72199    72200    +1     
  Branches     3352     3353    +1     
=======================================
+ Hits        70913    70917    +4     
+ Misses       1286     1283    -3     

Files	Coverage Δ
lib/datadog/appsec/configuration/settings.rb	99.14% <100.00%> (ø)
.../datadog/tracing/diagnostics/environment_logger.rb	97.36% <100.00%> (+0.03%)	⬆️
spec/datadog/appsec/configuration/settings_spec.rb	99.73% <100.00%> (ø)
...tadog/appsec/contrib/rack/gateway/response_spec.rb	100.00% <100.00%> (ø)
...adog/appsec/contrib/rack/reactive/response_spec.rb	100.00% <100.00%> (ø)

... and 4 files with indirect coverage changes

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[ivoanjo]

👍 LGTM