Update browser_tab.py

[Japan10]

Line: 915
Change "user-agent" to "User-Agent"

[codecov-io]

Current coverage is 85.62%

Merging #426 into master will decrease coverage by -0.09% as of 7355a3b

@@            master    #426   diff @@
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  Files           39      39       
  Stmts         4627    4627       
  Branches       633     633       
  Methods          0       0       
======================================
- Hit           3966    3962     -4
- Partial        156     159     +3
- Missed         505     506     +1

Review entire Coverage Diff as of 7355a3b

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[dvdbng]

Hi @Genius001 thanks for the pull request! There are some test failing because they have "user-agent" instead of "User-Agent" hardcoded in them, would you mind fixing that as well?

[Japan10]

Hi, @Youwotma

I noticed if change all 'user-agent' to 'User-Agent' in tests/test_execute.py that will cause another problem, And test will failing.

The error log https://travis-ci.org/scrapinghub/splash/jobs/118187194#L2146

I could not figure out how to resolve it.
If I fix all these headers key(cache-control, accept-encoding,accept-language) to case sensitive.
That could be affect other test file?

But this time I thought whether is it necessary to do this or keep original?

If it is necessary, workaround?