fix warnings generated because of connection leak

[aleerizw]

body should be closed

ref: square/okhttp#2311

Currently warnings are generated from okhttp:

com.spotify.githubclient.shade.okhttp3.internal.platform.Platform log
WARNING: A connection to https://ghe.spotify.net/ was leaked. Did you forget to close a response body?
To see where this was allocated, set the OkHttpClient logger level to FINE: Logger.getLogger(OkHttpClient.class.getName()).setLevel(Level.FINE);

[codecov]

Codecov Report

Merging #47 (fffd034) into master (27a77ca) will increase coverage by 2.86%.
The diff coverage is 76.92%.

@@             Coverage Diff              @@
##             master      #47      +/-   ##
============================================
+ Coverage     65.80%   68.66%   +2.86%     
- Complexity      176      195      +19     
============================================
  Files            30       32       +2     
  Lines           731      766      +35     
  Branches         29       33       +4     
============================================
+ Hits            481      526      +45     
+ Misses          229      217      -12     
- Partials         21       23       +2     

Impacted Files	Coverage Δ	Complexity Δ
...va/com/spotify/github/v3/prs/ReviewParameters.java	100.00% <ø> (+100.00%)	1.00 <0.00> (+1.00)
...m/spotify/github/v3/clients/PullRequestClient.java	26.41% <63.63%> (+26.41%)	5.00 <2.00> (+5.00)
...om/spotify/github/v3/clients/RepositoryClient.java	64.15% <66.66%> (+0.07%)	28.00 <1.00> (+1.00)
...va/com/spotify/github/v3/clients/GitHubClient.java	74.77% <80.00%> (+5.61%)	50.00 <11.00> (+9.00)
...com/spotify/github/v3/clients/GithubAppClient.java	75.00% <100.00%> (+3.57%)	4.00 <1.00> (+1.00)
...spotify/github/v3/prs/RequestReviewParameters.java	100.00% <100.00%> (ø)	1.00 <1.00> (?)
.../java/com/spotify/github/v3/prs/ReviewComment.java	100.00% <100.00%> (ø)	1.00 <1.00> (?)
... and 2 more

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