Fixed .podspec

We've made some changes on .podspec because it didn't work:
- After "pod install", tried to build and failed because the project didn't find libGameAnalytics. Cocoapods didn't download your static library. Now it's working.
- We've changed the name of podspec, for avoiding incompatibility in Cocoapods/specs's pull request because "GA-iOS-SDK" exists already (old SDK).