Unable to link github repository behind proxy
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## Description
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In our company we are unable to access to Github repositories trough command line without setting a proxy. 

## Version
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* Kactus:
0.3.19
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* Operating system:
macOS 10.14.3

## Steps to Reproduce
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ex,
1. `step 1`
2. `step 2`
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1. Create an empty repository on Github
2. Open Kactus
3. Click on "Select Repository"
4. Cut & paste the repository url
5. Try to connect...
### Expected Behavior
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I expect to connect correctly to my remote repository
### Actual Behavior
<!-- What actually happens -->
The system hang and after seconds stops with this error:

Cloning into '/Volumes/g08/02 - Documentazione di Progetto/2019/UX deliverable/Test/provakactus'...
fatal: unable to access 'https://github.com/charly71/provakactus.git/': Failed to connect to github.com port 443: Operation timed out

