MemoryLeakFix (#572)
MemoryLeakFix (#572)

* Added autorelease pool to prevent memory leak

Autorelease pool handles memory management for the `pcm: Data` object
created in the realtime audio input callback.

* Adjusted scope of autorelease pool for clarity

Includes explanatory comment

watson-developer-cloud/ios-sdk,tad-iizuka/swift-sdk,tad-iizuka/swift-sdk,watson-developer-cloud/ios-sdk,tad-iizuka/swift-sdk,tad-iizuka/swift-sdk,tad-iizuka/swift-sdk,watson-developer-cloud/ios-sdk,watson-developer-cloud/ios-sdk,watson-developer-cloud/ios-sdk