add method getPodSpecs and add related tests

[knight9999]

Platforms affected

ios

What does this PR do?

• Add new method getPodSpecs for PluginInfo class
• Add test code

See apache/cordova-discuss#108

What testing has been done on this change?

• npm run test

Checklist

• Reported an issue in the JIRA database
• Commit message follows the format: "CB-3232: (android) Fix bug with resolving file paths", where CB-xxxx is the JIRA ID & "android" is the platform affected.
• Added automated test coverage as appropriate for this change.

[codecov-io]

Codecov Report

Merging #48 into master will increase coverage by 0.15%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #48      +/-   ##
==========================================
+ Coverage   87.82%   87.98%   +0.15%     
==========================================
  Files          19       19              
  Lines        1799     1822      +23     
  Branches      373      377       +4     
==========================================
+ Hits         1580     1603      +23     
  Misses        219      219

Impacted Files	Coverage Δ
src/PluginInfo/PluginInfo.js	83.41% <100%> (+2.16%)	⬆️

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