Use of unresolved identifier 'LyftButton'

Nobody has claimed this yet.

I'm trying to use the SDK with Swift 4 and Xcode 9.3.

I had the same issue as #17, which I fixed by replacing lines 31 and 32 with:
```
var urlComponents = URLComponents(url: mutableURLRequest.url!, resolvingAgainstBaseURL: false)
var localVariable = urlComponents
urlComponents?.queryItems = (localVariable?.queryItems ?? []) + queryItems
```
Per [this SO post](https://stackoverflow.com/questions/46126574/overlapping-accesses-to-urlcomponents-but-modification-requires-exclusive-acc).

Now when I try to use `let lyftButton = LyftButton()`, I get the error "Use of unresolved identifier 'LyftButton'".

Is this SDK compatible with Swift 4 and Xcode 9.x? Also opened as a [SO post](https://stackoverflow.com/questions/50275835/syntax-errors-in-lyft-api-for-ios-wont-compile).

Start by reproducing `let lyftButton = LyftButton()` with Swift 4 and Xcode 9.3, then inspect the SDK's public API and usage documentation for the button type. Done means determining whether the SDK supports this toolchain and either restoring a compiling usage path or documenting the incompatibility.

Written by the indexing model from the issue text.