fix: calls ui apis on main thread

[sandmman]

Closes #123 moving this onto development.

Provides a fix for #869.

Issue

Updating UI apis from the background thread results in undefined behavior. This address the problem by moving the calls onto the main queue in the methods async block.

Testing

Ran a local iOS project using a local pod of BluemixAppID with xcode 9.

[coveralls]

Coverage decreased (-0.4%) to 82.067% when pulling 222f242 on issue.uiBackgroundThread into d924cf4 on development.

[sandmman]

@vitalymibm It turns out that our tests will almost always fail during peak hours on travis. It seems like a race condition exists between the simulator and our test cases that is exposed during slow cpu availability. I've been playing around with a couple fixes and will open another PR if one works. In any case, tests now pass.

Travis also no longer supports xcode 8.1, so I bumped the docs and travis to 8.3.

For the code coverage, I'm not sure why it doesn't count the lines in the DispatchQueue async code block when they clearly are called and do get counted by xcode's code coverage. Rather than add an arbitrary test case for some other unrelated block of code to offset the 0.4%, I think its best to leave it as is.

[vitalymibm]

@sandmman Ok, thank you for the info. I merged the PR.