Ignore issue if it is a Pull request

[Glennmen]

According to the Github API docs the Issues endpoint also returns Pull requests: https://developer.github.com/v3/issues/?q=is%3Aissue+is%3Aopen+sort%3Aupdated-desc#list-issues

This PR adds an extra filter that removes PR's from the list of Issues. More info can be found in the issue I made #72

Fixes #72

[codecov]

Codecov Report

Merging #73 into master will increase coverage by 0.03%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #73      +/-   ##
==========================================
+ Coverage   86.70%   86.73%   +0.03%     
==========================================
  Files          24       24              
  Lines         391      392       +1     
  Branches       80       80              
==========================================
+ Hits          339      340       +1     
  Misses         47       47              
  Partials        5        5              

Impacted Files	Coverage Δ
src/markdown/markdownIssues.js	100.00% <100.00%> (ø)

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[Glennmen]

Not sure if a test for this is needed. Let me know if I should add a test and how best add it (new test or adjust existing test).

[Glennmen]

@abhijeetps Can this PR get reviewed please?

[abhijeetps]

@Glennmen , thank you.
The PR looks good. I will test it in Weekly Digest Beta by the end of this month and I will let you know.
I have been a little busy lately so, I couldn't come up to check the PR. 😄
I'm really sorry for the delay.

[Glennmen]

@abhijeetps No problem! Glad to see that there is stil some activity in this useful project.
Let me know if you want me to change anything.

[Glennmen]

@abhijeetps Have you been able to test this PR yet?