SEGIntegration: Importing Context

[ghost]

What does this PR do?
This PR adds a missing import, which was causing a compiler warning, when using Segment Analytics via Carthage, in a project completely written in Swift.

Where should the reviewer start?

1. Check out this sample app
2. Run carthage bootstrap platform iOS
3. Build the sample project

As a result, you'll get the compiler warning mentioned above.

How should this be manually tested?
Yes!. Map the Sample App's Cartfile to giorgiopaoloni/analytics-ios branch dev instead, and verify the warning is gone. Note that your Cartfile should look as follows:

github "giorgiopaoloni/analytics-ios" "dev"

Any background context you want to provide?
Not really!

What are the relevant tickets?
N/A

Screenshots or screencasts (if UI/UX change)
N/A

Questions:

• Does the docs need an update?
  No need to.

• Are there any security concerns?
  No sir!

• Do we need to update engineering / success?
  No. Keep up the good work, thanks for helping us out!!

@segmentio/gateway

cc @fredrocious

[codecov-io]

Codecov Report

Merging #700 into dev will decrease coverage by 0.12%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##              dev     #700      +/-   ##
==========================================
- Coverage   72.52%   72.39%   -0.13%     
==========================================
  Files          39       39              
  Lines        1623     1623              
  Branches      171      171              
==========================================
- Hits         1177     1175       -2     
- Misses        329      331       +2     
  Partials      117      117

[f2prateek]

Sorry for the delay, thanks for this!