Fix JSON as on 27.11.2018

[SpEcHiDe]

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What is the purpose of your pull request?

• Bug fix
• Improvement
• New extractor
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Description of your pull request and other information

When the HotStar website was visited today, the JSON key seemed to have a changed.

Hence edited the one word in the code.

[dstftw]

PS C:\Dev\youtube-dl\master> py -3.6 -W error .\test\test_download.py TestDownload.test_HotStar
[hotstar] 1000076273: Downloading webpage
[hotstar] 1000076273: Downloading JSON metadata
[hotstar] 1000076273: Downloading m3u8 information
[info] Writing video description metadata as JSON to: test_HotStar_1000076273.info.json
.
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Ran 1 test in 6.333s

OK

Provide concrete example URLs of what this is supposed to fix.

[SpEcHiDe]

Please try with this URL: https://www.hotstar.com/1000057157 as shown in the screenshot.

[dstftw]

This change breaks current test as it has the old layout.